IMPROVEMENTS IN TELEPHONIC APPARATUS AND IN THE METHOD OF AND THE APPARATUS FOR TRANSMITTING ARTICULATE AND OTHER SOUNDS
Year: 1880

page_text: LETTERS PATENT to William Morgan-Brown, Patent Agent, of 38, Southampton
Buildings, London, for an Invention of "IMPROVEMENTS IN TELEPHONIC
APPARATUS AND IN THE METHOD OF AND THE APPARATUS FOR TRANSMITTING
ARTICULATE AND OTHER SOUNDS." A communication from abroad by
Alexander Graham Bell, of the City of Washington, District of Columbia,
United States of America.
PROVISIONAL SPECIFICATION left by the said William Morgan-Brown at
the Office of the Commissioners of Patents on the 25th September 1880.
WILLIAM MORGAN-BROWN, Patent Agent, of 38, Southampton Buildings, London,
"IMPROVEMENTS IN TELEPHOMIC APPARATUS AND IN THE METHOD OF AND THE
APPARATUS FOR TRANSMITTING ARTICULATE AND OTHER SOUNDS." [A commu-
nication from abroad by Alexander Graham Bell, of the City of Washington,
District of Columbia, United States of America.]
This Invention consists in a method of utilizing radiant energy and of applying
it by suitable apparatus to produce audible signals and to produce electric
signals.
The rays which proceed from the sun and other similar sources falling upon
various bodies produce effects generally perceived by the senses, as heat or as
color.
Besides this, and notably when they fall upon the substances hereinafter
mentioned, the energy which they are to convey produces in those bodies a change
which the sense of touch, or the sense of sight, has not been able to take notice
of; this changed condition may be fitly called a state of strain, and has been made
manifest in various ways in different substances.
This Invention relates to this class of changes.
The changes in the sensitive bodies employed in the apparatus hereinafter
described follow the changes in energy of the disturbing rays, following upon them
with such extreme rapidity that the two are substantially coincident in time as
compared with the time occupied by any vibrational movement which can be
detected by the ear; the extent of the change at each instant depends upon
variation in the amount of radiant energy expended upon the sensitive body at
that instant, and is approximately directly proportional thereto.

page_text: The change to a greater or less state of strain thus produced in the sensitive
body will therefore correspond with the variations in the disturbing cause, both in
extent and in rapidity of successions.
If, therefore, the energy of the rays acting on the sensitive body passes
alternately from a maximum to a minimum, that is, exhibits a variation of
a vibrational character, the changes in the sensitive body will be thereby
correspondingly controlled in their period of change, in their direction of change,
in their amplitude of total change, and also in the character of the changes which
take place while passing from a maximum to a minimum and back again, or, in
other words, the curve which graphically represents the changes thus caused in the
sensitive body will correspond to the curve which represents the variations in the
disturbing rays due to natural causes or which may be impressed upon them by
artificial means.
This Invention embodies a method and apparatus for impressing any variation
upon the rays or radiant energy falling upon the sensitive body; also a method
and an apparatus by which the changes in the sensitive body from a less to a
greater state of strain, and vice versa, can impart a corresponding motion to the
air.
If the changes succeed each other with sufficient rapidity, and possess sufficient
amplitude, the vibrational movements thereby imparted to the air become sensible
as sound waves, and a sound will be heard which will correspond in pitch to the
rapidity with which these changes succeed each other, in loudness to their extent,
and in "quality" to the character or vibrational form of the changes.
The radiant energy which affects the sensitive body may be varied in several
ways.
Its source may be controlled when, as in the case of a lamp, it is within reach of
an operator.
The rays which convey the energy may be controlled-in their passage from the
source to the sensitive body; for instance,-a-part.or_the_whole-may be intercepted_
by screens opaque to them, or the whole may have their energy diminished more:
or less by the interposition of substances which offer resistance to the passage
without wholly interrupting it, or they may be more or less concentrated upon or
diverted from the sensitive body by lenses, reflectors, or other appropriate means.
The sensitive body may be normally exposed to the full force of the rays and
then partially or wholly protected from them, and then partially or wholly exposed
to them; it may be normally partially exposed to their influence, and this exposure
may then be alternately increased or decreased.
In the forms of apparatus hereinafter described the desired variations in the
rays employed to effect the sensitive body are produced in these various ways by
means of motion imparted to the appropriate part of the transmitter; the extent
and characters of the changes thereby caused in the sensitive body depend upon
the extent and character of that motion, and consequently the sounds to which
these changes give rise depend for their pitch upon the frequency of that motion,
and for their "quality" upon the character of that motion.
When, therefore, as in certain forms of apparatus to be described, & sufficient
motion of the appropriate part of the transmitter is caused by the sound waves
which constitute vocal or other sounds acting upon a disc capable of vibrating, on
its equivalent, the character of notion thus taken up from the air at the
transmitting station causes vibrational changes of a corresponding character in the
sensitive body, and thereby produces vibrational movements of a corresponding
character in the air at the receiving station.
Thus a similar sound to that made or uttered at the transmitting station is heard
at the receiving station.
The receiving instrument consists of devices to receive the beam from the
transmitter and direct it upon the sensitive body together with the sensitive body
itself, and, when needed apparatus connected therewith to produce air vibrations
or sound waves.

page_text: An essential part of the receiver is the body sensitive to the rays which fall upon
it and the contrivances by which the disturbance therein produced by the rays is
made sensible.
There are several bodies whoso electric conductivity is varied by the rays which
fall upon them from the sun or other sources.
Any variation in the amount or in the intensity of the radiant energy so falling
upon them changes that conductivity or resistance; some of the apparatus
described uses this kind of sensitiveness to vary the current in a circuit which
includes the sensitive body and also includes a telephonic receiver, which will
thereupon give forth a sound whose character or "quality" will correspond to the
character of the said variations.
Selenium, when in the proper state, is the body which has been found most
effective for this purpose, this Invention including also a process of preparing the
selenium, as hereinafter described.
It has also been discovered that various substances, especially hard rubber in thin
sheets, say, from the thickness of an ordinary telephone diaphragm up to three
millimeters, is so sensitive that when the sun rays, concentrated by lenses or
reflectors, are allowed to fall upon it, and these ray's aro.: rapidly interrupted, the
ear placed in contact with or in close proximity to the hard rubber will hear
proceeding from it a sound whose pitch varies with the frequency of the
interruptions and corresponds to the frequency.
Audible results have been obtained by using as a receiver a disc of hard rubber,
as described, and plates of gold, silver, platinum, aluminium, iron, steel, antimony,
lead, Babbit's metal, Jenks steam packing, tinned iron, tin foil, brass, copper,
German silver, ordinary telephone diaphragms.
These were formed into plates of the size and thickness of the ordinary hand
telephone diaphragms.
Similar results have been obtained with plates of mica, paper, different kinds of
wood, patent leather, vulcanized fibre, celuloid, ivory, silvered glass, and other
substances.
The receiver may be made in the form of a tube. In this case the light in the
form of a converging pencil is thrown in at one end, so as to reach a focus near
the entering end, and thence diverging so as to strike the inside of the tube; the
operator listens at the other end. The tube serves as a resonater, and greatly
amplifies the effect of interruptions. whoso frequency correspond with the normal
pitch of the tube.
Audible results have been obtained with tubes of soft vulcanized rubber, of
brass, soft wood, about one half inch in diameter, or less.
Certain forms of apparatus embodying this Invention will next be described.
The apparatus employed consists essentially of an instrument which varies the
amount of radiant energy falling upon the sensitive body.
This part of the apparatus will be called the photophonic transmitter.
Of an instrument by which the variations produced in the sensitive body are
directly or indirectly made sensible, as sound without the intervention of electricity,
or as electrical variations, which are capable of producing sounds or signals by
means of an electric speaking telephone receiver or other suitable electric signalling
instrument; this part of the apparatus will be called a photophone receiver, and of
various devices for giving the proper direction or diffusion to the rays employed.
These instruments must be suitably arranged and placed with reference to each
other.
The beam controlling apparatus has been mentioned as the photophone trans-
mitter, and the sensitive body and parts connected with it as the photophone
receiver, and this is true if the action of the beam itself is chiefly considered.
But considering that form of apparatus shown which employs electricity as a
modified electric speaking telephone, the beam controller, the beam, and the
electrical sensitive body may properly be called a variable resistance speaking
0

page_text: telephone transmitter, operating to create electrical undulations by means of sound
waves, and the receiving telephone the receiver thereof.
If the rays are to pass over any considerable distance they should, to obtain
the best result, be formed into a parallel pencil in order to prevent dispersion and
loss of effect.
At the point they are to be controlled by the transmitter they are preferably
concentrated in order that a large amount of energy may be readily controlled
there, and this concentration may be wholly or partially continued till they reach
the sensitive body; or they may be there again concentrated, so as to exercise
their full effect on a small surface, which is important in most forms of apparatus.
This management of the rays may be effected by well known refractory and
reflecting devices, the arrangement of which will be sufficiently apparent from the
descriptions of apparatus hereinafter given.
Similar devices will serve to direct the rays into the most convenient path, and
it will be noticed hereafter that in one of the most efficient forms of transmitter
the power of a reflector to change the direction of the rays by changing the
inclination of the whole or any part of its surface is employed.
Figure 1 is a general diagraphic view of a transmitting and receiving photophonic
apparatus embodying my Invention in what is found to be a simple and effective
arrangement for the production of a musical sound or note, and Figure 2 is a
detail thereof illustrating the interrupter employed in this instance.
A ray from the sun is caused to take a proper direction in any suitable manner;
in this case by reflecting it from a plane mirror or heliostat a into a condensing
apparatus.shown as a lens v, which should be aplanatic and achromatic to prevent
dispersion, and which brings the beam to a focus, as at-2.
A suitable screen, as a solution of alum in a glass cell a, for example, to obstruct
the passage of obscure-heat-rays-without-obstructing the passage of light may be
-used-to-protect the apparatus from the affect of heat when the sunlight is used.
It is found with certain forms of receiving instruments-employing-selenium--
such a heat screen does not to any great extent diminish the effect produced.
The passage of the rays at the point 2 may be interrupted or controlled in any
suitable manner, as, for instance, by an interrupting wheel or disc o pivotted on
an axle d, so that the periphery of the said disc lies in the path of the rays; and
at or near the focus 2 this disc is provided with a series of openings or holes 3
(see Figure 2) lying in the range of the pencil of rays at or near the focal
point 2.
As the wheels c is rotated the rays will intermittingly pass through the holes 3,
and then be cut off by the blank spaces between the said holes, which blank should
be at least as large as the sectional area of the beam at the point 2 to ensure its
complete interception; a series of alternate impulses and interruptions will thus be
produced, constituting what may be termed an intermittent beam; this beam
passes on from the focal point 2, and may be directed to any desired point.
The rays which diverge from the focal point 2 are again brought to the condition
of a parallel pencil by the lens d¹, and thence pass to the receiving instrument e,
shown in this instance as a thin disc or diaphragm f of hard rubber placed in a
suitable frame or enclosing case g, and which, as herebeforo stated, will be affected
by the intermittent beam falling on it in such manuer as to produce sound waves,
the rapidity or pitch of which corresponds to the rapidity of interruption of the
said beam caused by the disc c.
The diaphragm f may be placed in a suitable sound chamber furnished with a
sound passage or ear piece, shown as a flexible tube h, by which the sound may be
conducted to the ear of the listener.
A condensing instrument, shown as a lens i, is preferably used to concentrate
the rays and increase their effect in the diaphragm f. The said condenser should
be as large as possible, as the beam of light is somewhat dispersed in traversing
any considerable distance.

page_text: It is obvious that other forms of receiving instruments may be used in connection
with the above described transmitter; or that this receiving instrument may be
used with other forms of transmitting instrument. Various modifications of both
of these will be hereinafter described.
By varying the velocity of the rotation of the disc c the rapidity of interruption
of the beam will be correspondingly varied, and consequently the pitch of the
sound produced at the receiving station.
In this form of transmitter the notion which causes the interruptions is
continuously in the same direction.
Other forms are devised to use instead of it, in which the screens employed
operate by a to and fro or vibratory motion given to the moving parts thereof.
By means of these it is enabled to give a new power and capacity to the apparatus.
Figures 4, 5, 6, 7, are such forms of apparatus.
Figure 4 represents two gratings of which one is fixed, while the other is
moveable, and adapted to slide to and fro upon the fixed grating.
In the condition shown in the Drawing the opaque portion of one half overlaps
and partially covers the open slit in the other, and a passage equal to about one
half the slit is afforded for the passage of the rays.
If the moveable grating is moved slightly upward, the space allowed for the rays
is diminished or entirely cut off; if it be moved slightly downward the space is
increased, and if that motion extends through a distance equal only to half the
width of the narrow slit, the space allowed for the rays is doubled, and the increase
or diminution will be directly proportional to the amplitude of the motion.
Such gratings may be constructed with actual open slits, as shown in Figure 4,
or they may be made of glass covered with an opaque coating (silver, for example),
which may be scraped off in strips to form the slits, the latter boing more con-
venient.
If desired the opaque portions may be polished, and the rays reflected therefrom
employed to affect the receiving instrument, the maximum amount being reflected
when the polished portion of one grating is opposite the slits or unpolished portion
of the other, so that the rays are reflected from the whole surface of both, and the
minimum effect is when the polished portion of one is behind that of the other, and
thus rendered inoperative for reflecting.
In some instances both gratings inay be made movable, in which case they
should be so arranged that any actuating impulse would move them in opposite
directions.
In the form of intercepter or beam-controller, illustrated in Figures 5, 6, 7, &
series of slats m of opaque material are pivotted, as at 5, in a frame-work in the
path of the rays, the said slats being all oscillated simultaneously like the slats of a
window-blind by a rod connecting with the actuating vibrator at j; as shown in
Figure 6, the rod n is connected with all the slats on the same side of their pivotted
points, so that they are all moved parallel, but in Figure 7 the alternate slats are
connected with the rod n on the opposite sides of their pivots, so that the alternate
slats incline in opposite directions as they are closed.
These slats in their normal position close about one half the space, as shown in.
the main Figures 6, 7, (the rays passing in the direction of the arrow) and by their
moven.ent in one direction they increase the open space for the rays to pass until
they arrive at the position shown at 6, where the maximum amount is allowed to
pass, while a movement in the other direction decreases the amount until, in the
position shown at 7, the rays are wholly intercepted.
It will be seen that when the slats are open, as shown at 6, they only present
their edges as obstruction to the rays, and their thickness may be much less than
the open space between them, so that a greater amount of rays may be allowed to
pass than when the gratings shown in Figures 3 and 4 are used, as they never
allow more than half the beam to pass.
By connecting the rods n nearer the pivots 5 the same extent of movement in
their rods will give a greater angular movement to the slats. It will be seen that

page_text: none of these forms of screens or interruptions will give an intermittent beam, as
herein described, unless they are wholly closed at each vibration, but if there be
any vibration at all, the strength, and consequently the effects, of the pencil of rays
which pass beyond the instrument, though never wholly interrupted, will vary in
accordance with the period and with the amplitude of vibrational movement of the
moving part of the transmitter.
These vibrations in the strength of the total beam falling upon the sensitive
body employed in the receiver will cause in its condition changes, which in their
rapidity of succession and in their extent will correspond to the vibrational
movenient in the transmitter.
When these changes are made sensible as sound, the pitch and loudness of that
sound will be controlled by the period and the amplitude of the motion given to
the vibrational part of the transmitter.
There are many ways in which vibratory motion can be communicated to these
or other forins of screen; for example, the moving portion being made as light as 1
possible can be attached, as shown in Figure 2, to a tuned reed j, which may be
moved by an electro-magnet either directly by an automatic circuit breaker, or by
an electric current controlled by any of the well known devices for interrupting or
varying a current, or an organ reed may be employed; in every such case the
sound produced at the receiving station will correspond in pitch and in loudness to
the period of vibration and to the amplitude of vibration of this transmitting reed.
Figure 8 shows photophonic apparatus by which articulate speech may be
transmitted. It has been already stated that the sound at the receiving station,
due to the effect produced by the rays which reach the sensitive body there placed,
-corresponds to the character of the changes in the energy of the pencil of rays
which reach it.
The herein before described_transmitters have been intended to control merely
the pitch and the loudness of a simple musical note, and the devices in them bave
therefore been adapted to merely control the period during which the energy-of-
the beam passes from its maximum to its minimum and the range of its change,
or the difference of energy between its maximum and minimum.
or
In order to transmit articulate speech, or any sound having a complex character
'quality," it is further necessary, first, that the proper character shall be
impressed upon the changes in the receiver, upon the variations in the rays, and
upon the motion which produces them while passing from one extreme to the
other, and, second, that the voice of the speaker or the sounds to be transmitted
shall of themselves operate the photophonic transmitter, and impress their own
character or form of vibration upon the moveable part of the apparatus which
controls the beam.
In the apparatus, Figure 8, the movable part of a screen grating k, l, like that
shown in Figure 4, is attached to the centre of a diaphragm v constructed mounted,
and arranged in a sound chamber as is usual in electric speaking telephone
transmitters. When spoken to, this diaphragm and the movable part of the screen
attached thereto take up from the sound waves the peculiar character of vibration
due to the "quality" of the sound uttered; the same character of vibration change
is thereby imparted to the pencil of rays which passes through the instrument, and
by them to the sensitive body in the receiving instrument, where it is made
sensible by a sound of corresponding quality, and the words uttered into the
transmitter are heard to proceed from the receiver.
It is well known that the extent of motion which can be given by the voice to
a diaphragm, and the parts directly connected with it, is quite small. By making
the slits or openings in the screen small a slight extent of motion will cause a great
percentage of change, i.e., from an almost total interruption to the passage of one
half of the rays; and by suitable means the rays can be so concentrated that this
range of variation will produce a great absolute change in the radiant energy
falling on the sensitive body. In passing the rays through fine slits, however

page_text: some difficulties arise in the nature of interference. These have been obviated by
another form of articulate speech transmitter, which will presently be described.
In Figure 8 the radiant body is shown as the flame of a candle p, and the lens b
brings the divergent rays thereof to the condition of a parallel beam, which is
controlled by the grating k, l.
Another method is to bring the rays to a focus 2 (Figure 9), and instead of the
grating k, l, employ two plates k, l, one fixed and the other connected to the
vibrator or diaphragm o, the said plates having a hole 8 of the size and form of the
image at the focal point, and the hole of the fixed grating coinciding with said
image in position to allow all the rays to pass through it. The movable plate in
passing to and from a position with its hole coinciding with that of the fixed plate,
allows or obstructs the passage of a greater or less portion of the pencil of rays.
which are then directed to and act upon the receiving instrument, as in the other
cases described.
A single plate constructed in this manner when properly guided will operate in
the same way, and by giving such a plate a movement parallel to the axis of the
pencil of rays, it will intercept an increasing portion thereof as it moves from the
focal point, and thus control the beam.
The receiver, which is shown in Figure 8, depends upon the property herein before
referred to as belonging to certain substances, notably properly prepared
selenium, of undergoing a great instantaneous and substantially proportional increase
of conductivity when acted upon by the rays proceeding from the sun and other
similar sources.
A piece of selenium S, brought into a suitable condition and suitably mounted,
forms a part of an electric circuit, supplied with a current by a constant electro-
motive force, as by the battery B; this selenium is exposed to the rays which
proceed from the transmitter, and every variation caused in its conductivity
produces a corresponding variation in the strength of the current; these variations
will, in the manner now well known to electricians, operate an electric speaking
telephone receiver T (or other sensitive electrical instrument) placed in the circuit
or connected with it, and this telephone receiver will give forth the articulate words
which have been uttered into the photophonic transmitter.
Selenium, as ordinarily found in the market, and in the state or condition
assumed by it when solidified in the ordinary manner from a molten state, is
found to be of extremely high resistance to an electric current, and only slightly
sensitive to or affected by rays falling upon it.
The description of methods of treating selenium hitherto published have
disclosed a long and apparently uncertain process of treatment, by which the
product obtained is not always uniform in nature, and apparently does not possess
the desired properties of conductivity and sensitiveness to the action of rays in so.
high a degree as was the product derived by the method of treatment set forth in
the following description, and based on the novel discovery that the non-
conducting selenium that has solidlified from a state of fusion, and which has a
black color and lustrous surface, undergoes, when its temperature is gradually
raised, a structural or molecular change when the temperature reaches a certain
point, about 117°C. This change is apparent to the eye by an alteration in
external appearance which accompanies it. When the change is about to take
place, or as it takes place, a sort of cloudiness is seen to pass over the surface,
which loses its dark color and lustre and assumes a bluish color and rather dull
appearance, somewhat like tarnished silver or lead.
The electric conductivity of the selenium is at the same time suddenly increased,
as may be observed by a galvanometer in circuit with the said selenium.
Upon continuing to raise the temperature the conductivity also increases, as may
be observed by the further deflection of the galvanometer needle, and this increase
continues until the selenium reaches a temperature of about 217° C., at which it is
about to fuse but has not actually melted. If allowed to melt it would again loose

page_text: its conductivity and become in solidifying, as before described, dark colored and
not sensitive to light.
When properly cooled from the said temperature, it retains or assumes, when
cooled, the desired conductivity and sensitiveness. The novel process consists in
gradually heating the selenium to be treated in an apparatus in which its surface
can be readily observed, or in which its conductivity can be indicated, as by a
galvanometer, or both, and just at the point when the selenium is beginning to
fuse, and before it actually melts, in removing the source of heat and allowing the
selenium to cool.
It is sometimes desirable to repeat the process.
The construction of the apparatus for heating the selenium will vary according
to the size and shape of the selenium to be treated. To prepare it for use in the
cells hereinafter described, the instrument containing the selenium to be treated
may be placed on a metal plate over a gas flame, and at the moment the point
of fusion is reached the supply of gas is cut off and the instrument allowed to cool.
The heating has been spoken of as gradual, but the entire operation of heating and
cooling of these small masses of inetal need occupy only a few minutes.
The proper moment for stopping the heating operation may be known by the
galvanometer needle; its increase of deflection at that moment ceases, and the
amount of deflection begins to decrease; it may also very conveniently be known
by observing the surface, which becomes dark, loses its metallic lustre, and changes
from a leaden color to a blackish or nearly black color,
For treating large masses of selenium a closed chamber may be used, to ensure
that the entire mass shall be uniformly heated, and any convenient source of heat
be employed.
Such a chamber may be provided with windows for observation. It is necessary
that the action of the heat should be under perfect control, so that no further
heat may be added after the temperature at which fusion begins has been reached.
A-thermometer may be employed to enable the temperature to be observed, to
thus warn the operator of-the-approach-of-the-moment-when special care is to be¯
exercised.
It will be understood that selenium assumes the desired properties when heated
to any temperature in the range between the point at which the described
molecular or structural change takes place and the point of fusion; but these
properties exist to the greatest extent when the upper limit of the the said range
of temperature is attained.
It is obvious that when the the desired temperature is reached, the selenium
may be removed from the source of heat instead of cutting off the supply of fuel as
described.
As the selenium, even when in its most favorable condition, is of high resistance,
it is desirable to interpose it in the circuit in the form of a conductor of but slight
length and of large area, which may be done very advantageously by some novel
forms of cells to be hereinafter described.
Some of the best forms of apparatus for this purpose consist generically of two
or more plates of good conducting metal separated by a thin sheet of insulating
material placed between each pair of plates. This insulating sheet has a slightly
smaller surface than the conducting plates, and the space thus left is filled up with
the selenium, which thus serves as a conductor between the two plates. It is
obvious that this construction enables the selenium to be used in the shape of a
conductor of large area, nearly all of which is exposed to the rays, and of
an extremely short length, equal to the thickness of the insulator, which may
conveniently be a sheet of mica, while it uses very little selenium, and it is very
easy to work the solenium into this shape by heating the metal cell and fusing the
selenium into the cavity left between the two plates when the insulator is placed
between them.
A considerable number of these cells may be built up side by side and connected
in parallel branch circuits.
5

page_text: Besides mica, the paints which are employed in painting on china may be used
to separate the metal plates; when baked, as the plates are heated the said paint
becomes porcelain. Various forms of cell constructed on this plan will bo
hereinafter described; other forms of cells are described on a plan alightly
different from this.
The electric circuit being under control of the selenium resistance therein, and
the selenium under control of the pencil of rays, and the rays under the control of
the transmitting instruments, it is obvious that any instruments which can be
controlled by slight variations in an electric circuit, such as, for instance, the usual
telephone instruments, if placed in the electric circuit with the said selenium will
be controlled by and will emit sounds corresponding to the action of the said
transmitting apparatus on the beam which falls on the selenium.
Figure 10 illustrates another apparatus for transmitting complex sounds or
articulate speech. As in the form last described, the sound words due to the voice
serve. to give to the movable part of the transmitter a vibrational movement of
corresponding character, and this movement in turn impresses a vibrational or
alternate variation of corresponding character upon the amount of radiant energy
falling upon the sensitive body of the receiver.
The pencil of rays is passed through a suitable concentrating apparatus a (shown
here as a lens), and also through a heat absorbing apparatus a¹, which prevents the
heat rays from warping the reflector of the transmitter.
It then falls upon a reflector r, shown as a plane reflector, placed at such an angle
as to direct the rays to the receiver e.
After leaving this reflector the rays may be caused to pass through a lens № in
order to give them the desired parallelism, if they do not already possess it. In
the Drawing they are shown more concentrated on the reflector 7 than in their
path from the transmitter to the receiver. Arrived there they are caused to fall
upon the sensative receiver either directly, or, as in the Drawing, after further
concentration by the mirror 8.
Tracing the path of a single ray from the lens a and cell a', it will be seen that
its path from the reflector will depend upon the angle at which that portion of
the reflector on which it falls is presented to it.
If the reflector be so placed normally that the
will pursue
ray
the path towards
the receiver shown in the Drawing, then a slight change in the angle of incidence
of that particular ray will, if in one direction, so alter the subsequent path of the
ray as to divert it from the receiver, or if in the other direction will direct upon
the receiver rays which otherwise might not have reached it.
Any such change will therefore vary the amount of radiant energy exerted upon
the receiver.
This reflector is made of some material, such as glass (silvered) or well polished
metal, which will take up from the sound waves of the air their peculiar motion
and vibrate in accordance with them as truly as the diaphragm of a speaking
telephone does.
As it vibrates each portion of it deflects from its normal position as part of a
plane surface, and bends or tips more or less in one direction or the other, conse-
quently each ray reflected from it is more or less diverted from its normal path,
and thereby the total amount of radiant energy exerted on the sensitive receiver by
all the rays reflected from the transmitter varies at each instant.
The extent of variation from instant to instant, the direction of the variation, the
period of cach variation, and the character of each variation depends upon the
vibrational movement of the transmitting reflector which causes the changes, and
therefore the same character of vibrational movement given to the transmitter by
the voice reappears in the vibrations in the radiant energy operative upon the
sensitive part of the receiver, and consequently in the sound or other effects due to
the changes in that sensitive body. The words spoken against the transmitter are
thereupon heard to proceed from the receiver.
Articulate speech has thus been transmitted, using as reflector a disk of silvered

page_text: glass 30 inches in diameter, of tolerable thickness; and clearer and better articu-
Tation has been obtained by using as a reflector a disc of thin glass, such as used for
mounting objects for the microscope, properly silvered, and about two inches in
diameter.
↑
In the Drawing the reflector is shown as mounted in a mouth-piece, such as is
commonly used in telephones; it is essential that the mouth piece should be so
fixed and the reflector so held in it that its normal position should always remain
the same in relation to the source of rays and the receiver in order that the rays
may be directed to the receiver.
It will sometimes be desirable, as when the radiant source is movable, or the
same transmitter is to be used with receivers at different points, to mount the
transmitter so as to give it a universal movement. A mounting similar to that of
a telescope of a surveyors transit accomplishes this, and a similar graduated limb is
often useful. The mouth piece or round passage may be made as a flexible tube to
enable it to be readily used with the mirror r in any desired angular position.
A small telescope attached to the instrument may be used as a finder.
The beam after passing from the controlling or transmitting apparatus is received,
as in the other form described, upon a collecting and condensing instrument, shown
in this instance as a parabolic mirror s, by which the rays are concentrated on a
selenium cell S' of peculiar construction, as will be hereinafter described; the said
cell is placed at the focal point of the said mirror 8, and is adjusted in position as
shown; it is supported at the end of the tube t, passing through a socket at the
vertex of the mirror, and kept in adjusted position therein by a set screw u.
The electrodes 11, 12, pass through the said tube, and may be connected with a
battery and telephonic or electrical instrument, as before described in connection
with Figure 8.
A small telescope or "finder" w may be employed to enable the operator to give
the proper direction for the axis of the mirror, or this may be done by sighting
through the tube t.
A simple form of selenium-cell-S-is-shown-in plan-and-section Figures 11 and 12,
and the different parts thereof in Figure 10. This cell has an arrangement similar
to, but in construction is different from, what is known as Siemens spiral. Two
ribbons a², b², of suitable conducting material, preferably brass, form the terminals
of the poles of the battery B, the said ribbons being separated by thin strips c² of
suitable insulating material, which is slightly narrower than the metal strip, so as
to leave a slight open space between the edges of said strips.
The whole is then coiled into a flat spiral in order to give it a more convenient
form for exposure to the action of the rays, and strip d' of insulating material being
interposed to prevent conductive contact between the consective coils of the
spiral.
The said coil is then heated to a temperature slightly higher than the melting
point of selenium, and solid selenium rubbed over its surface. The selonium melts,
filling the channels between the metallic ribbons, and forming a connection between
them, as shown at c².
Ribbons of mica may be used as the insulating material to separate the plates, or
they may be coated with enamel paints or japan varnish, in which case a further
amount of metal may be electro-deposited on the edges of the strips to give them
the proper saliense or to form suitable channels for the reception of the selenium.
Another form of selenium cell is illustrated in plan and section Figures 14, 15.
In this case the conducting and insulating materials are arranged in alternate
parallel strips a³, b, c, d, and only the alternate strips 3 of the insulating material
have a smaller extent of surface than the enclosing metal strips, so that the
selenium deposited as before described in the channels left for it will connect
only alternate pairs of the said strips, that is, connect each strip 6s with the strip a³
on one side thereof, but not with the strip a³ on its other side.
The strips as all project on one side and are electrically connected by the rod ³,
and the strips b³ are connected on the other side by the rod g³, and connected

page_text: set of strips with one pole of the battery, or, in other words, placed in a circuit
which is completed by the selenium 12.
Another forin of cell used by me, and shown in plan and section Figures 16, 17,
consists essentially of a metal box at and plate c' of glass fitted in the top of and
resting on an armature shoulder in the said box.
A disc b' of metal is attached to the under side of the glass plate, and is slightly
smaller than the internal diameter of the box, and consequently completely insulated
therefrom.
The said disc b is provided with a series of tapering holes 20, and the bottom
of the box with a series of pins 21 of slightly smaller diameter than the holes, so
that when in place the said pins pass into the said holes leaving a narrow annular
space around each pin.
The box is inverted and these annular spaces are filled with pulverized selenium e²,
which is then melted and annealed or properly treated to thus close the circuit
between the box and disc.
Another cell which has been used with excellent results is shown at S in
Figure 10), and in side and end views on a larger scale in Figures 18 and 19, and
in detail in Figures 20, 21, 22, 23, 24.
The principle of construction is similar to that of the cell described in connection
with Figure 14, but the surface to be exposed is cylindrical instead of plane, such
form being preferable when used in connection with a parabolic mirror as the
instrument for condensing rays.
Instead of rectangular strips of conducting and insulating material, circular
discs a, b, c, are used; those marked c of insulating material are slightly smaller
in diameter than those a, b, of conducting material, so that annular channels. arc
left between the edges of the conducting discs a, b, around the periphery of the
insulating discs c", and in this instance such chaunels are left between all tho said
discs a, b, so that each disc a will be connected by the adjacent annular rings c²
of selenium with both the discs on either side.
The discs are each provided with a central hole 25 to enable them to be held in
proper position by a mandrel, where they are clamped between two suitable end
plates,, the discs of metals and insulating material being alternated on said
mandrel.
The conducting discs are electrically connected together in two sets of alternate
plates a, b, between which the circuit is completed by the annular rings of
selenium e² following the channels around the discs of insulating material c³.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said William Morgan-Brown in the Great Seal Patent Office on the 24th
March 1881.
WILLIAM MORGAN-BROWN, Patent Agent, of 38, Southampton Buildings, London.
* IMPROVEMENTS IN TELEPHONIC APPARATUS AND IN THE METHOD OF AND THE
APPARATUS FOR TRANSMITTING ARTICULATE AND OTHER SOUNDS." A commu-
nication from abroad by Alexander Graham Bell, of the City of Washington,
District of Columbia, United States of America.
This Invention consists in a method of utilizing radiant energy, and of applying
it by suitable apparatus to produce audible signals and to produce electric signals;
also in the herein described method of signaling or communicating, which consists
in controlling a beam of rays as to its amount or active strength in accordance
with the signals to be given, and receiving the said rays on a sensitive substance
forming a part of an electric circuit, and affected as to its resistance in accordance
with the amount or strength of the beam received upon it, whereby electric 1
apparatus in the said circuit may be controlled to give signals corresponding to
the controlling influence imparted to the beam.
That improvement in the art or method of transmitting or reproducing sound,
which consists in giving a beam of rays an undulating or intermittent character in
accordance with the sound waves it is desired to produce, and providing a receiving a
_apparatus, adapted. when- acted--upon-by the said rays to produce-air vibrations-or
sound waves corresponding to the undulations or variations in the said beam,
substantially as hereinafter described.
The herein described method of and apparatus for transmitting articulate and
-other-sound-by-causing-in-the-rays-proceeding-from-a-photophonic-transmitting-
instrument to a photophonic receiver undulatory variations in radiant energy,
similar in form to the sound waves accompanying said articulate and other
sounds.
The herein described method of producing sounds of any desired pitch, amplitude,
and quality by exposing a body sensitive to radiant energy to rays, whose effective 3
energy exercised upon said sensitive body is caused to vary in accordance with
the vibrational form of the sound waves appropriate to the sound to be produced.
The herein described method of and apparatus for transmitting articulate and
other sounds by causing the sound waves which constitute said sounds to produce
similar variations in the beam of rays proceeding from a photophonic transmitter 3
to a photophonic receiver; also,
In an apparatus for communicating signals, a beam-controlling apparatus to
impart a varying character to a beam of rays (from a radiant body), and a receiving
apparatus sensitive to the said bean, and operated thereby to give signals corre-
sponding to the variations in the said beam imparted by the controlling apparatus. 4
Controlling in a photophonic transmitter the amount of radiant energy passing
from it by means of motion imparted to its moving portion.
The employment in an apparatus for sound transmission of a beam-controlling
device, itself actuated by the waves which constitute said sound, to give the beain
an undulating character or variations in effective strength similar in form to the
said sound waves, as hereinafter described.
The combination in a photophonic transmitter of a movable and an immovable
portion to control the amount of radiant energy passing from it, substantially as
hereinafter described.
The herein described method of controlling the amount of radiant energy passing 5
from a photophonic transmitter by the extent and character of the motion imparted
to the moving part thereof.

page_text: The herein described method of controlling the amount of radiant energy passing
from a photophonic transmitter in accordance with the form of the sound waves
accompanying the sound to be transmitted, by actuating the moving portion of such
transmitter by the sound waves themselves, either directly or through the inter-
vention of an electric speaking telephone apparatus.
The combination with a transmitting apparatus, to give a beam from a radiant
body an undulatory character or variations in effective strength, of a receiving
apparatus sensitive to the said bean, and having the property of emitting sound
under the influence and corresponding to the character of the said beam, sub-
stantially as hereinafter described.
In the employment in an apparatus for sound transmission of a transmitting
apparatus to control a beam from a radiant body, and a receiving apparatus con-
taining as a portion of an electric circuit n device, the electrical condition of which
is varied in accordance with the strength or character of the beam affecting it
and the telephonic instruments in circuit therewith, substantially as hereinafter
described.
The employment in an apparatus for sound transmission of a beam of rays
from a radiant body, and an elastic reflector to control the said beam, acted upon
by sound waves and changed in form thereby, to thus cause the direction of tho
rays reflected therefrom to be changed, and their effect in a sensitive receiving
body to be varied in accordance with the said sound waves.
The employment in an instrument containing selenium as a portion of an electric
circuit of two or more strips of conducting material separated by insulating
material arranged to leave a portion of the space between the said strips unoccupied
thereby, and selenium placed in the said unoccupied space to complete an electric
circuit between the said conducting strips.
The employment in an instrument containing selenium as a portion of an electric
circuit of two pieces of conducting material insulated from one another, and
provided with a series of points near but not in contact with one another, and
selenium placed between the said portions of conducting material at the said points
to electrically connect them.
The herein described process of treating selenium, which consists in raising its
temperature until a structural change, made apparent by an alteration in the
appearance of its surface, as described, and by its increased electric conductivity,
takes place, substantially as hereinafter described.
That improvement in the art or method of treating selenium which consists in
heating the selenium to raise its temperature to the point at which fusion begins,
and allowing it to cool without fusion, all as and for the purpose hereinafter set
forth.
That improvement in the art or method of treating selenium which consists in
applying heat thereto in an apparatus in which the selenium is visible to the
operator, to thereby enable tho said operator to observe any changes in the selenium
that are made manifest in the external appearance thereof, substantially as herein-
after described.
The rays which proceed from the sun and other similar sources falling upon
various bodies produce effects generally perceived by the senses, as heat or as
color.
Besides this, and notably when they fall upon the substances hereinafter
mentioned, the energy which they are to convey produces in those bodies a change
which the sense of touch or the sense of sight has not been able to take notice of ;
this changed condition may be fitly called a state of strain, and has been made
manifest in various ways in different substances.
This Invention relates to this class of changes.
The changes in the sensitive bodies employed in the apparatus hereinafter
described follow the changes in energy of the disturbing rays, and follows them
with such extreme rapidity that the two are substantially coincident in time, as
compared with the time occupied by any vibrational movement which can be

page_text: detected by the ear; the extent of the change at each instant depends upon
variation in the amount of radiant energy expended upon the sensitive body at
that instant, and is approximately directly proportional thereto.
The change to a greater or less state of strain thus produced in the sensitive
body will therefore correspond with the variations in the disturbing cause, both in
extent and in rapidity of successions.
If therefore the energy of the rays acting on the sensitive body passes alternately
from a maximum to a minimum, that is, exhibits a variation of a vibrational
character, the changes in the sensitive body will be thereby correspondingly
controlled in their period of change, in their direction of change, in their amplitube
of total change, and also in the character of the changes which take place while
passing from a maximum to a minimum and back again, or, in other words, the
curve which graphically represents the changes thus caused in the sensitive body
will correspond to the curve which represents the variations in the disturbing rays
due to natural causes, or which may be impressed upon them by artificial means.
This Invention embodies a method and apparatus for impressing any variation
upon the rays or radiant energy falling upon the sensitive body, also a method and
an apparatus by which the changes in the sensitive body from a less to a greater
state of strain, and vice versa, can impart a corresponding motion to the air.
If the changes succeed each other with sufficient rapidity, and possess sufficient
amplitude, the vibrational movements thereby imparted to the air become sensible
as sound waves, and a sound will be heard which will correspond in pitch to the
rapidity with which these changes succeed each other, in loudness to their extent,
and in "quality" to the character or vibrational form of the changes.
The radiant energy which affects the sensitive body may be varied in several
ways.
Its source may be controlled when, as in the case of a lamp, it is within reach of
an operator.
The rays which convey the energy may be controlled-in-their-passage-from-the-
-source-to-the-sensitive-body-;- for instance,.a.part.or_the_whole_may_be_intercepted
by screens opaque to them, or the whole may have their energy diminished more
or less by the interposition of substances which offer resistance to the passage
without wholly interrupting it, or they may be more or less concentrated upon or
divested from the sensitive body by lenses, reflectors, or other appropriate means.
The sensitive body may be normally exposed to the full force of the rays, and
then partially or wholly protected from them; or it may be normally protected
from the rays and then partially or wholly exposed to them; it may be normally
partially exposed to their influence, and this exposure may then be alternately
increased or decreased.
In the forms of apparatus hereinafter described, the desired variations in the rays
employed to affect the sensitive body are produced in these various ways by means
of motion imparted to the appropriate part of the transmitter; the extent and
characters of the changes thereby caused in the sensitive body depend upon the
extent and character of that motion, and consequently the sounds to which theso
changes give rise depend for their pitch upon the frequency of that motion, and
for their "quality" upon the character of that motion.
When therefore, as in certain forms of apparatus to be described, a sufficient
motion of the appropriate part of the transmitter is caused by the sound waves
which constitute vocal or other sounds acting upon a disc capable of vibrating, or
its equivalent, the character of motion thus taken up from the air at the trans-
mitting station causes vibrational changes of a corresponding character in the
sensitive body, and thereby produces vibrational movements of a corresponding
character in the air at the receiving station.
Thus a similar sound to that made or uttered at the transmitting station is
heard at the receiving station.
The receiving instrument consists of devices to receive the beam from the trans-
mitter, and direct it upon the sensitive body, together with the sensitive body

page_text: itself, and, when needed, apparatus connected therewith to produce air vibrations
or sound waves.
An essential part of the receiver is the body sensitive to the rays which fall
upon it, and the contrivances by which the disturbance therein produced by tho
rays is made sensible.
There are several bodies whose electric conductivity is varied by the rays which
fall upon them from the sun or other sources.
Any variation in the amount or in the intensity of the radiant energy so falling
upon them changes that conductivity or resistance; some of the apparatus
described uses this kind of sensitiveness to vary the current in a circuit which
includes the sensitive body, and also includes a telephonic receiver, which will
thereupon give forth a sound whose character or "quality" will correspond to the
character of the said variation.
Selenium, when in the proper state, is the body which has been found most
effective for this purpose, this Invention; this Invention including also a process of
preparing the selenium, as hereinafter described.
It has also been discovered that various substances, especially hard rubber in thin
sheets, say, from the thickness of an ordinary telephone diaphragm up to three
millimeters, is so sensitive that when the sun rays concentrated by lenses or
reflectors are allowed to fall upon it, and these rays are rapidly interrupted, the car
placed in contact with or in close proximity to the hard rubber will hear proceeding
from it a sound, whose pitch varies with the frequency of the interruptions, and
corresponds to the frequency.
Audible results have been obtained by using as a receiver a disc of hard rubber,
as described, and plates of gold, silver, platinum, aluminium, iron, steel, antimony,
lead, Babbit's-metal, Jenk's steam-packing, tinned iron, tin foil, brass, copper,
Gerinan silver, ordinary telephone diaphragins.
These were formed into plates of the size and thickness of the ordinary hand
telephone diaphragms.
Similar results have been obtained with plates of mica, paper, different kinds of
wood, patent leather, vulcanized fibre, celluloid, ivory, silvered glass, and other
substances.
The receiver may be made in the form of a tube. In this case the light in the
form of a converging pencil is thrown in at one end so as to reach a focus near the
entering end, and thence diverging so as to strike the inside of the tube. The
operator listens at the other end. The tube serves as a resonator and gently
amplifies the effect of interruptions, whose frequency correspond with the normal
pitch of the tube.
Audible results have been obtained with tubes of soft vulcanized rubber, of
brass, and of soft wood about one half inch in diameter or less.
Certain forms of apparatus embodying this Invention will next be described.
The apparatus employed consists essentially of an instrument which varies the
amount of radiant energy falling upon the sensitive body.
This part of the apparatus will be called the photophonic transmitter.
Of an instrument by which the variations produced in the sensitive body are
directly or indirectly made sensible as sound without the intervention of electricity,
or as electrical variations, which are capable of producing sounds or signals by
means of an electric speaking telephone receiver, or other suitable electric signalling
instrument; this part of the apparatus will be called a photophone receiver, and of
various devices for giving the proper direction or diffusion to the rays employed.
These instruments must be suitably arranged and placed with reference to each
other.
The beain-controlling apparatus has been mentioned as the photophone trans-
mitter, and the sensitive body and parts connected with it as the photophone
receiver, and this is true if the action of the beam itself is chiefly considered.
But considering that form of apparatus shown which employs electricity, as
a modified electric speaking telephone, the beam-controller, the beam, and the

page_text: electrically sensitive body may properly be called a variable resistance speaking
telephone transmitter operating to create electrical undulations by means of sound
waves, and the receiving telephone the receiver thereof.
If the rays are to pass over any considerable distance they should, to obtain the
best result, be formed into a parallel pencil in order to prevent dispersion and loss
of effect.
At the point they are to be controlled by the transmitter they are preferably
concentrated in order that a large amount of energy may be readily controlled
there; and this concentration may be wholly or partially continued till they
reach the sensitive body, or they may be there again concentrated so as to
exercise their full effect on a small surface, which is important in most forms of
apparatus.
This management of the rays may be effected by well known refracting and
reflecting devices, the arrangement of which will be sufficiently apparent from the
descriptions of apparatus hereinafter given.
Similar devices will serve to direct the rays into the most convenient path, and
it will be noticed hereafter that in one of the most efficient forms of transmitter
the power of a reflector to change the direction of the rays by changing the
inclination of the whole or any part of its surface is employed.
Figure 1 is a general diagraphic view of a transmitting and receiving photophonic
apparatus embodying my Invention in what is found to be a simple and effective
arrangement for the production of a musical sound or note, and Figure 2 is a detail
thereof illustrating the interruptor employed in this instance.
A ray from the sun is caused to take a proper direction in any suitable manner;
in this case by reflecting from a plane mirror or heliostat a into a condensing
apparatus, shown as a lens b, which should be aplanatic and achromatic to prevent
dispersion, and which brings the beam to a focus as at 2.
A suitable screen, as a solution of alum in a glass cell a¹, for example, to obstruct
--the-passage-of-obscure-heat-rays-without-obstructing-the-passage.of.light may be.
used to protect the apparatus from the effect of heat when the sun light [is used.
It is found with certain forms of receiving instruments employing selenium such a
heat screen does not appreciably diminish the effect produced.
The passage of the rays at the point 2 may be interrupted or controlled in any
suitable manner, as, for instance, by an interrupting wheel or disc e pivoted on an
axle d, so that the periphery of the said disc lies in the path of the rays, and
at or near the focus 2 this disc is provided with a series of openings or holes 3
(see Figure 2), lying in the range of the pencil of rays at or near the focal
point 2.
As the wheel c is rotated the rays will intermittingly pass through the holes 3,
and then be cut off by the blank spaces between the said holes, which blank spaces
should be at least as large as the sectional area of the beam at the point 2 to ensure
its complete interception; a series of alternate impulses and interruptions will thus
be produced, constituting what may be termed an intermittent beam; this beam
passes on from the focal point 2, and may be directed to any desired point.
The rays which diverge from the focal point 2 are again brought to the condition
of a parallel pencil by the lens d', and thence pass to the receiving instrument e,
shown in this instance as a thin disc or diaphragm of hard rubber placed in a
suitable frame or enclosing case g, and which, as herebefore stated, will be affected
by the intermittent beam falling on it in such manner as to produce sound waves,
the rapidity or pitch of which corresponds to the rapidity of interruption of the
said beam caused by the disc c.
The diaphragm fmay be placed in a suitable sound chamber furnished with a
sound passage or ear piece, shown as a flexible tubo h, by which the sound may
be conducted to the ear of the listener.
A condensing instrument, shown as a lens i, is preferably used to concentrate
the rays, and increase their effect on the diaphragm ; the said condenser should

page_text: be as large as possible, as the beam of light is somewhat dispersed in traversing
any considerable distance.
It is obvious that other forms of receiving instruments may be used in connection
with the above described transmitter, or that this receiving instrument may be used
with other forms of transmitting instrument; various modifications of both of these
will be hereinafter described.
By varying the velocity of the rotation of the disc c the rapidity of interruption
of the beam will be correspondingly varied, and consequently the pitch of the sound
produced at the receiving station.
In this form of transmitter the motion which causes the interruptions is con-
tinuously in the same direction.
Other forms are devised to use instead of it, in which the screens employed
operate by a to and fro or vibratory motion given to the moving parts thereof.
By means of these it is enabled to give a new power and capacity to the apparatus.
Figures 4, 5, 6, 7, are such forms of apparatus.
Figure 4 represents two gratings , l, of which one, k, is fixed, while the other, l,
is movable, and adapted to slide to and fro upon the fixed grating.
In the condition shewn in the Drawing the opaque portion of one half overlaps
and partially covers the open slit in the other, and a passage equal to about one
half the slit is afforded for the passage of rays.
If the movable grating is moved slightly upward the space allowed for the rays
is diminished or entirely cut off; if it be moved slightly downward the spaco is
increased, and if that motion extends through a distance equal only to half the
width of the narrow slit the space allowed for tho rays is doubled, and the increase
or diminution will be directly proportional to the amplitude of the motion.
Such gratings may be constructed with actual open slits, as shown in Figure 4,
or they may be made of glass covered with an opaque coating (silver, for examplo),
which may be scraped off in straps to form the slits, the latter being more
convenient.
If desired the opaque portions may be polished and the rays reflected therefrom
employed to affect the receiving instrument, the maximum amount being reflected
when the polished portion of one grating is opposite the slits or unpolished portion
of the other, so that the rays are reflected from the whole surface of both, and the
minimum effect is when the polished portion of one is behind that of the other,
and thus rendered imperative for reflecting.
In some instances both gratings may be made movable, in
should be so arranged that any actuating impulse would move
directions.
which case they
them in opposito
In the form of interceptor or beam-controller, illustrated in Figures 5, 6, 7, a
series of slats m of opaque material are pivoted, as at 5, in a frame-work in the
path of the rays, the said slats being all oscillated simultaneously like the slats of
a window blind by a rod n connecting with the actuating vibrator j; as shown in
Figure 6, the rod n is connected with all the slats on the same side of their pivoted
points, so that they are all moved parallel; but in Figure 7 the alternate slats are
connected with the rod m. on the opposite sides of their pivots, so that the alternate
slats incline in opposite directions as they are closed.
These slats in their normal position close about one half the space, as shown in
the main, Figures 6, 7 (the rays passing in the direction of the arrow), and by their
movement in one direction they increase the open space for the rays to pass until
they arrive at the position shown at 6, where the maximum amount is allowed to
pass, while a movement in the other direction decreases the amount until in the
position shown at 7, the rays are wholly intercepted.
It will be seen that when the slats are open, as shown at 6, they only present
their edges as obstruction to the rays, and their thickness may be much less than
the open space between them, so that a greater amount of rays may be allowed to
pass than when the gratings shown in Figures 3 and 4 aro usod, as the letter never
allow more than balf the beam to pass.

page_text: By connecting the rods n nearer the pivots 5 the same extent of movement in
their rods will give a greater angular movement to the slats. It will be seen that
none of these forms of screens or interruptions will give an intermittent beam, as
herein before described, unless they are wholly closed at each vibration; but if
there be any vibration at all the amount or strength, and consequently the effect
of the pencil of rays which pass beyond the instrument, though never wholly
interrupted, will vary in accordance with the period and with the amplitude of
vibrational movement of the moving part of the transmitter.
These vibrations in the strength of the total beam falling upon the sensitive body
employed in the receiver will cause in its condition changes, which in their rapidity
of succession, and in their extent, will correspond to the vibrational movement in
the transmitter.
When these changes are made sensible as sound, the pitch and loudness of that
sound will be controlled by the period and the amplitude of the motion given to
the vibrational part of the transmitter.
There are many ways in which vibratory motion can be communicated to these
or other forms of screen; for example, the moving portion, being made as light as
possible, can be attached, as shown in Figure 2, to a tuned reed j, which may be
moved by an electro-magnet, either directly, as an automatic circuit breaker, or by an
electric current controlled by any of the well known devices for interrupting or
varying a current, or an organ-reed may be employed; in every such case the
sound produced at the receiving station will correspond in pitch and in loudness to
the period of vibration and to the amplitude of vibration of this transmitting reed.
Figure 8 shows photophonic apparatus, by which articulate speech may be
transmitted. It has been already stated that the sound at the receiving station,
due to the effect produced by the rays which reach the sensitive body there placed,
corresponds to the character of the changes in- the energy of the pencil of rays
which reach it.
The herein before described transmitters have been intended to control merely the
pitch and the loudness of a simple musical note, and the devices in them have
therefore been adapted to merely control-the-period-during-which-the-energy-of-
the beam passes froin its maximum to its minimum, and the range of its change or
the difference of energy between its maximum and minimum.
or
In order to transmit articulate speech, or any sound having a complex character
"quality," it is further necessary, first, that the proper character shall he
impressed upon the changes in the receiver, upon the variations in the rays, and
upon the motion which produces them while passing from one extreme to the other;
and, second, that the voice of the speaker or the sounds to be transmitted shall of
themselves operate the photophonic transmitter and impress their own character
or form of vibration upon the movable part of the apparatus which controls the
beam.
In the apparatus, Figure 8, the movable part of a screen grating k, l, like that
shown in Figure 4, is attached to the centre of a diaphragm o, constructed, mounted,
and arranged in a sound chamber, as is usual in electric speaking telephone
transmitters. When spoken to, this diaphragm, and the movable part of the screen
attached thereto, take up from the sound waves the peculiar character of vibration
due to the "quality" of the sound uttered, the same character of vibrational
change is thereby imparted to the pencil of rays which passes through the
instrument, and by them to the sensitive body in the receiving instrument, where
it is made sensible by a sound of corresponding quality, and the words uttered
into the transmitter are heard to proceed from the receiver.
It is well known that the extent of motion which can be given by the voice to
a diaphragm, and the parts directly connected with it, is quite small.
By making the slits or openings in the screen small, a slight extent of motion
will cause a great percentage of change, i.e., from an almost total interruption to the
passage of one half of the rays; and by suitable means the rays can be so
concentrated that this range of variation will produce a great absolute change in

page_text: the radiant energy falling on the sensitive body. In passing the rays through fine
slits however some difficulties arise in the nature of interference. These have
been obviated by another form of articulate speech transmitter, which will presently
be described.
In Figure 8 the radiant body is shown as the flame of a candle p, and the lens b
brings the divergent rays thereof to the condition of a parallel beam, which is
controlled by the grating k, l.
Another method is to bring the rays to a focus 2 (Figure 9), and instead of the
grating k, l, employ two plates k, l, one fixed and the other connected to the
vibrator or diaphragm o, the said plates having a hole 8 of the size and form of
the image at the focal point, and the hole of the fixed grating coinciding with
said image in position to allow all the rays to pass through it. The movable
plate in passing to and from a position, with its hole coinciding with that of the
fixed plate, allows or obstructs the passage of a greater or less portion of the pencil
of rays which are then directed to and act upon the receiving instrument, as in the
other cases described.
A single plate constructed in this. manner, when properly guided, will operate in
the same way, and by giving such a plate a movement parallel to the axis of the
pencil of rays it will intercept an increasing portion thereof as it moves from tho
focal point, and thus control the beam.
The receiver, which is shown in Figure 8, depends upon the property, herein-
before referred to, as belonging to certain substances, notably, properly prepared
selenium, of undergoing a great, instantaneous, and substantially proportional
increase of conductivity when acted upon by the rays proceeding from the sun
and other similar sources.
A piece of selenium S brought into a suitable condition and suitably mounted,
forms a part of an electric circuit supplied with a current by a constant electro
motive force, as by the battery B; this selenium is exposed to the rays which
proceed from the transmitter, and every variation caused in its conductivity
produces a corresponding variation in the strength of the current; these variations
will, in the manner now well known to electricians, operate an electric speaking
telephone receiver T (or other sensitive electrical instrument) placed in the circuit
or connected with it, and this telephonic receiver will give forth the articulate
words which have been uttered into the photophonic transmitter.
Selenium, as ordinarily found in the market and in the state or condition
assumed by it when solidified in the ordinary manner from a molten state, is
found to be of extremely high resistance to an electric current, and only slightly
sensitive to or affected by rays falling upon it.
The description of methods treating selenium bitherto published have disclosed
a long and apparently uncertain process of treatment, by which the product
obtained is not always uniform in nature, and apparently does not possess the
desired properties of conductivity and sensitiveness to the action of rays in
so high a degree as does the product derived by the method of treatment set
forth in the following description, and based on the novel discovery that the
non-conducting selenium that has solidified from a state of fusion, and which has
a black colour and lustrous surface, undergoes when its temperature is gradually
raised a structural or molecular change when the temperature reaches a certain
point about 117° C. This change is apparent to the eye by an alteration in
external appearance which accompanies it. When this change is about to take
place, or as it takes place, a sort of cloudiness is seen to pass over the surface,
which loses its dark color and lustre, and assumes a bluish color and rather dull
appearance, somewhat like tarnished silver or lead.
The electric conductivity of the selenium is at the same time suddenly increased,
as may be observed by a galvanometer in circuit with the said selenium.
Upon continuing to raise the temperature the conductivity also increases, as may
be observed by the further deflection of the galvanometer needle, and this increase
continues until the selenium reaches a temperature of about 207° C., at which it

page_text: is about to fuse, but has not actually melted. If allowed to melt it would again
lose its conductivity and become, on solidifying, as before described, dark colored
and not sensitive to light.
When properly cooled from the said temperature, it retains or assuines when
cooled the desired conductivity and sensitiveness. The novel process consists
in gradually heating the selenium to be treated in an apparatus in which its
surface can be readily observed, or in which its conductivity can be indicated, as
by a galvanometer, or both, and just at the point when the selenium is beginning
to fuse and before it actually melts, in removing the source of heat and allowing
the selenium to cool.
It is sometimes desirable to repeat the process.
The construction of the apparatus for heating the selenium will vary according
to the size and shape of the selenium to be treated. To prepare it for use in the
cells hereinafter described the instrument containing the selenium to be treated
may be placed on a metal plate over a gas flame, and at the moment the point of
fusion is reached the supply of gas is cut off and the instrument allowed to cool.
The beating has been spoken of as gradual, but the entire operation of heating
and cooling of these small masses of metal need occupy only a few minutes.
The proper moment for stopping the heating operation may be known by the
galvanometer needle; its increase of deflection at that moment ceases and the
amount of deflection begins to decrease; it may also very conveniently be known
by observing the surface, which becomes dark, loses its metallic lustre, and changes
from a leaden color to a blackish or nearly black color.
For treating large masses of selenium a closed chamber may be used to ensure
that the entire mass shall be uniformly heated and any convenient source of heat
be-employed.
Such a chamber may be provided with windows for observation.
It is necessary_that_the_action_of_the_heat.should-be-under-perfect-control,.so.
that no further heat may be added after the temperature at which fusion begins
has been reached.
A thermometer may be employed to enable the temperature to be observed, to
thus warn the operator of the approach of the moment when special care is to be
exercised.
It will be understood that selenium assumes the desired properties when heated
to any temperature in the range between the point at which the described molecular
or structural change takes place and the point of fusion, but these properties exist
to the greatest extent when the upper limit of the said range of temperature is
attained.
It is obvious that when the desired temperature is reached the selenium may be
removed from the source of heat instead of cutting off the supply of fuel, as
described.
As the selenium, even when in its most favorable condition, is of high
resistance, it is desirable to interpose it in the circuit in the form of a conductor of
but slight length and of large arca, which may be done very advantageously by
some novel forms of cells to be hereinafter described.
Some of the best forms of apparatus for this purpose consist generically of two or
more plates of good conducting metal, separated by a thin sheet of insulating
material placed between each pair of plates. This insulating sheet has a slightly
smaller surface than the conducting plates, and the space thus left is filled up with
the selenium, which thus serves as a conductor between the two plates. It is
obvious that this construction enables the selenium to be used in the shape of a
conductor of large area, nearly all of which is exposed to the rays and of an
extremely short length, equal to the thickness of the insulator, which may
conveniently be a sheet of mica, while it uses very little selenium, and it is very
easy to work the selenium into this shape by heating the metal cell and fusing the
selenium into the cavity left between the two plates when the insulator is placed
between them.

page_text: A considerable number of these cells may be built up side by side and connected
in parallel branch circuits.
Besides mica, the paints which are employed in painting on china may be used to
separate the metal plates; when baked as the plates are heated the said paint
becomes porcelain. Various forms of cell constructed on this plan will be
hereinafter described. Other forms of cells are described on a plan slightly different
from this.
The electric circuit being under control of the selenium resistance therein, and
the selenium under control of the pencil of rays, and the rays under the control of
the transmitting instrument, it is obvious that any instruments which can be
controlled by slight variations in an electric circuit, such as, for instance, the usual
telephone instruments, if placed in the electric circuit with the said selenium, will
be controlled by and will emit sounds corresponding to the action of the said
transmitting apparatus on the beam which falls on the selenium.
Figure 10 illustrates another apparatus for transmitting complex sounds or
articulate speech. As in the form last described, the sound waves due to the voice
serve to give to the moveable part of the transmitter a vibrational movement of
corresponding character, and this movement in turn impresses a vibrational or
alternate variation of corresponding character upon the amount of radiant energy
falling upon the sensitive body of the receiver.
The pencil of rays is passed through a csuitable concentrating apparatus a (shown
here as a lens), and also through a heat absorbing apparatus a', which prevents the .
heat rays from warping the reflector of the transmitter.
It then falls upon a reflector 7 shown as a plane reflector r, placed at such an
angle as to direct the rays to the receiver e.
After leaving this reflector the rays may be caused to pass through a lens & in
order to give them the desired parallelism, if they do not already. possess it. In the
Drawing they are shown more concentrated on the reflector 7 than in their path
from the transmitter to the receiver. Arrived there they are caused to fall upon
the sensitive receiver, either directly, or, as (in the Drawing after further cop-
centration by mirror 8.
Tracing the path of a single ray from the lens a and cell a¹, it will be scen
that its path from the reflector will depend upon the angle at which that portion
of the reflector 7 on which it falls is presented to it.
If the reflector be so placed normally that the ray will pursue the path towards
the receiver shown in the Drawings, then a slight change in the angle of incidence
of that particular ray will, if in one direction, so alter the subsequent path of the
ray as to divert it from the receiver; or if in the other direction, will direct upon
the receiver rays which otherwise might not have reached it.
Any such change will therefore vary the amount of radiant energy exerted upon
the receiver.
This reflector T is made of some material, such as glass (silvered), or thin polished
metal, which will take up from the sound waves of the air their peculiar inotion,
and vibrate in accordance with thom, as truly as the diaphragm of a speaking
telephone does.
As it vibrates, each portion of it departs from its normal position as part of a
plane surface, and bends or tips more or less in one direction or the other,
consequently each ray reflected from it is more or less diverted from its normal
path, and thereby the total amount of radiant energy exerted on the sensitive
receiver by all the rays reflected from the transmitter varies at each instant.
The extent of variation from instant to instant, the direction of the variation,
the period of each variation, and the character of each variation, depends upon
the vibrational movement of the transmitting reflector which causes the changes,
and therefore the same character of vibrational movement given to the transmitter
by the voice, re-appears in the vibrations in the radiant energy operative upon the
sensitive part of the receiver, and consequently in the sound or other effects due to

page_text: material have a smaller extent of surface than the enclosing metal strips, so that
the selenium e, deposited as before described in the channels left for it, will
connect only alternate pairs of the said strips, that is, connect each strip b³ with
the strip a³ on one side thereof, but not with the strip a³ on its other side.
The strips as all project on one side, and are electrically connected by the rod f³,
and the strips 63 are connected on the other side by the rod g³, and each connected
set of strips with one pole of the battery, or, in other words, placed in a circuit
which is completed by the selenium e².
Another form of cell used by me, and shown in plan and section, Figures 16, 17,
consists essentially of a metal box a* and plate c' of glass fitted in the top of and
resting on an annular shoulder in the said box.
A disc b of metal is attached to the under side of the glass plate, and is slightly
smaller than the internal diameter of the box, and consequently completely
insulated therefrom.
The said disc b✶ is provided with a series of tapering holes 20, and the bottom of
the box with a series of pins 21 of slightly smaller diameter than the holes, so that
when in place the said pins pass into the said holes, leaving a narrow annular
space around each pin.
The box is inverted, and these annular spaces are filled with pulverized
selenium e, which is then melted and annealed, or properly treated to thus close
the circuit between the box and disc.
Another cell,which has been used with excellent results is shown at S in Figure 10,
and in side and end views on a larger scale in Figures 18 and 19, and in detail in
Figures 20, 21, 22, 23, 24.
The principle of construction is similar to that of the cell described in connection
with Figure 14, but the surface to be exposed is cylindrical instead of plane, such
form being preferable when used in connection with a parabolic mirror as the
instrument for condensing rays.
Instead of rectangular strips of conducting and insulating material, circular
discs a, b, c, are used. Those marked c³ of insulating material are slightly
smaller in diameter than those a, b, of conducting material, so that annular channels
are left between the edges of the conducting discs a, b, around the periphery of
the insulating discs c³, and in this instance such channels are left between all tho
said discs a, b, so that each disc a³ will be connected by the adjacent annular
rings e of selenium with both the discs b' on either side.
The discs are each provided with a central hole 25 to enable them to be held in
proper position on a mandrel, where they are clamped between two suitable end
plates, the discs of metal and insulating material being alternated on said
mandrel.
The conducting discs are electrically connected together in two sets of alternate
plates a, b, between which the circuit is completed by the annular rings of
selenium e, following the channels around the discs of insulating material c³.
This connection is accomplished as follows:-The discs are provided with holes,
shown as four in number. In the conducting discs two of the holes 30, 31, are of
larger diameter than the other two 32, 33, which are of the same size, as all four of
the holes in the insulating discs.
In placing the discs on the mandrel the holes are all placed with their centres in
line, and the large holes 30, 31, of each conducting disc are in line with the sinall
holes 32, 33, of the conducting discs on each side of it; or, in other words, in a given
line of holes all those of the plates a³ will be of different diameter from those of the
plates b³.
A cylinder of conducting material, of a diameter equal to that of the small holes
driven through a line of holes, will touch and electrically connect the alternate
conducting plates having their small holes in that line, and will not touch the other
plates.
Two of the cylinders f³ will connect together all the discs of one set, as a³, which
will form one terminal of the circuit, and the other two cylinders g³ will connect

page_text: the discs of the other set 56, which will form the other terminal, but the two sets
a³, b³, will be connected only by the selenium e³.
In order to ensure a more perfect connection between the plates a³ and cylinders ƒ³,
and the plates b³ and cylinders g³ are made tubular, and one or more slots 40 cut
longitudinally through their sides.
Washers c of insulating material are placed within the large boles 30, 31, in the
conducting discs, so that the said washers completely insulate and separate that
portion of the said discs from the cylinders.
Melted conducting material, as for example, type metal, is poured into the
tubes f, g, and passing through the longitudinal slots makes a perfect connection 1
with the plate having small holes 32, 33, around the said tubes, as shown in Figure 23,
where the type metal is indicated by the letter f7, but is prevented by the
washers c from making a contact with the plates having the large holes adjacent
to it, as shown in Figure 22.
Instead of the washers c of insulating material, smaller washers or rings of any
material, as for instance metal, may be used to confine the molten metal and prevent
its contact with the plates at the large holes, the said rings themselves being too
small in external diameter to touch the said discs.
Instead of using molten metal in the tube to form the connection, pulverized
conducting material may be used, as, for example, metal filings, spelter formning 2
an excellent connector, and in such case the cell is much more readily taken apart.
Nuts on the ends of the tubes f, g, serve to hold the whole together.
The cell is heated and the selenium melted thereon, and in all cases better results
have been obtained by filing off the selenium which covered the edges of the con-
ducting discs or strips, and leaving only the selenium between the said conducting 2
strips or discs.
After the surface is finished the mandrel, if of conducting material, should be
removed and a handle or tube t may be screwed into one of the end plates h³, as
the means for holding the cell in position.
— Au-alum-cell has-been-placed-in-the-path-of tho pencil so that the rays which 3
operated the instrument were other than heat rays.
Audible effects have been produced with a selenium cell receiver when the alum
cell was removed, and a thin sheet of hard rubber substituted therefor sensibly
opaque to light, and also when both the rubber and the alum cell were placed in
the path of the rays.
The Invention therefore is not limited to any portion of the rays which proceed
from the sun or other similar bodies.
The apparatus has been denominated a photophone because an ordinary beam of
light contains rays which are practically operative.
3
It should be remarked, however, that cutting off the luminous rays of the sun 4
which have passed through the lenses, as by a solution of iodine in bisulphide of
carbon, stops the operation of the apparatus.
The rays of gas, of a petroleum lamp, and of a candle, and of the lime light
have been employed with a selenium cell, and for many purposes, an artificial
source of light, the position of which can be adjusted at pleasure and kept 4
unchanged and unaffected by night or weather, is more convenient than sunlight.
Prepared selenium has been described as a type of one class of sensitive bodies
whose changed condition is manifested by the variation in the resistance they
afford to a constant current, and a disc of hard rubber as a type of another class
of bodies, the changes in which can become directly audible as sound.
Forms of apparatus have been described in which the radiant energy falling
upon a sensitive body operates to vary the resistance of the circuit of which it
forms part; others to vary the electro-motive force of current in the circuit.
5
The strength of the electric current in the receiving circuit may also be varied
by varying the electro motive force developed in the circuit.
5
Thus, for instance, a thermopile, when used as the sensitive part of the receiver,
would also be directly affected by heat rays, and would give rise to varying

page_text: currents in a circuit in which it was placed; but in order that tones may be so
produced, the thermopile must not be merely sensitive but much more rapid in its
action than those ordinarily known.
Rays of light as distinguished from rays of heat will develope an electric current
when falling upon the junction of two different metals when reduced to the form
of thin films.
Light falling on sensitive selenium will also develope a current capable of giving
electric signals. In both these contrivances, however, special rapidity of action, as
well as great sensitiveness, is required.
A beam of heat rays, by falling upon a material arranged to absorb them
quickly and again cool quickly, as fine wires strained, may be made to exhibit
its variations.
The amount of rays allowed to act on the receiver may be modified by controlling
the source from which they are derived, instead of intercepting or deviating them
in their path; the well known manometric flame apparatus is suitable for this
purpose. The motion required to operate such a flame apparatus may be given, as
is well known, by the voice.
The supply of gas for a burner may be allowed to pass through a grating similar
to that shown in Figure 4, and when the moveable part is vibrated the supply of
gas will be controlled accordingly.
The beam may pass from the transmitting to the receiving instrument by other
than direct paths if necessary, and for this suitable reflectors or other directing
instrument may be employed.
The instrument may be arranged with reference to each other according to tho
uses desired to be made of them. The transmitter and the sensitive body may be
placed near together, or be separated by any distance over which the rays can pass
effectively.
If a transmitter be moved by an electric current, the surface which carries that
current may be of any desired length, and arranged in any appropriate way
known to clectricians.
If an electrically sensitive receiver be used, as, for example, a selenium cell, the
circuit which contains it may be extended to any suitable distance, or may be
connected with another circuit by induction coils in a manner and for purposes
well known to electricians, and to those who are familiar with variable resistance
electric speaking telephones.
Inasmuch as the rays have no inertia and are inflexible, a slight motion of a
reflector, such, for example, as it will receive if attached to the diaphragm of a
receiving telephone, can not only be made to manifest itself as light (as in a
reflecting galvanometer) but also as sound, or as a variation of an electric current
in a secondary or local circuit supplied with its own battery.
The sound produced in the receiving telephone is a function which is affected by
at least three variables, namely, the character of the disturbing rays, or of their
source; the character of the variation in the part of those rays; the character of
the sensitive body.
In the apparatus shown in the Drawings when mounted for use, as thero
arranged, the second element is all that varies, and the others remain constant; in
one form mentioned, in which the source of rays is a manometric flame, the
variation is in the source itself, the path of the rays remaining unchanged.
But it is obvious that when one element is removed and replaced by a different
one, e. g., when one sensitive body is replaced by another, one source of radiant
energy by another, one partially intercepting body by another, the other elements
remaining the same, this change will produce a corresponding change in the audible
results, and can be detected by the sense of hearing.
Having now described and particularly set forth the nature of the said Invention
and the manner of carrying the same into effect, I would have it understood
that what I claim is,-
1st. The herein described method of signalling or communicating which consists

page_text: in controlling a beam of rays, as to its amount or active strength in accordance
with the signals to be given, and receiving the said rays on a sensitive substance
forming a part of an electric circuit, and affected as to its resistance in accordance
with the amount or strength of the beam received upon it, whereby electric
apparatus in the said circuit may be controlled to give signals corresponding to
the controlling influence imparted to the beam.
2nd. That improvement in the art or method of transmitting or reproducing sound,
which consists in giving a beam of rays an undulating or intermittent character in
accordance with the sound waves it is desired to produce, and providing a receiving
apparatus adapted, when acted upon by the said rays, to produce air vibrations or
sound waves, corresponding to the undulations or variations in the said beam,
substantially as described.
3rd. The herein described method of and apparatus for transmitting articulate
and other sound by causing, in the rays proceeding from a photophonic transmitting
instrument to a photophonic receiver, undulatory variations in radiant energy
similar in form to the sound waves accompanying said articulate and other
sounds.
4th. The herein described method of producing sound of any desired pitch,
amplitude, and "quality," by exposing a body sensitive to radiant energy to rays
whose effective energy exercised upon said sensitive body is caused to vary in
accordance with the vibrational form of the sound waves, appropriate in the sound
to be produced.
5th. The herein described method of and apparatus for transmitting articulate
and other sounds, by causing the sound waves which constitute said sounds to
produce similar variations in the beam of rays proceeding from a photophonic
transmitter to a photophonic receiver.
6th. In an apparatus for communicating signals, a beam controlling apparatus, to
import a varying character to a beam of rays (from a radiant body), and a receiving
apparatus_sensitive_to__the_said_beam, and operated thereby to give signals
corresponding to the variations in the said beam imparted by the controlling
apparatus.
7th. In a photophonic transmitter, controlling the amount of radiant energy
passing from it by means of motion imparted to its noving portion.
8th. In an apparatus for sound transmission, a beam controlling device, itself
actuated by the waves which constitute said sound, to give the beam an undulatory
character or variations in the effective strength, similar in form to the said sound
waves, substantially as described.
9th. In a photophonic transmitter, the combination of a moveable and immoveablo
portion to control the amount of radiant energy passing from it, substantially as
described.
10th. The herein described method of controlling the amount of radiant energy
passing from a photophonic transmitter, by the extent and character of the motion
imparted to the moving part thereof.
11th. The herein described method of controlling the amount of radiant energy
passing from a photophonic transmitter, in accordance with the form of the sound
waves accompanying the sound, to be transmitted by actuating the moving portion
of such transinitter by the sound waves themselves, either directly or through the
intervention of an electric speaking telephone apparatus.
12th. The combination with a transmitting apparatus to give a beam from a
radiant body, an undulatory character or variations in effective strength, of a 5
receiving apparatus sensitive to the said beam, and having the property of
emitting sound under the influence and corresponding to the character of the
said beam, substantially as described.
13th. In an apparatus for sound transmission, a transmitting apparatus to
control a beam from a radiant body, and a receiving apparatus containing as a 5
portion of an electric circuit a device, the electrical condition of which is varied

page_text: in accordance with the strength or character of the beam affecting it, and tele-
phonio instruments in circuits therewith, substantially as described.
14th. In an instrument containing selenium as a portion of an electric circuit,
two or more strips of conducting material separated by insulating material arranged
to leave a portion of the space between the said strips unoccupied thereby, and
selenium placed in the said unoccupied space to complete an electric circuit between
between the said conducting strips, substantially as and for the purpose described.
15th. In an apparatus for sound transmission, a beam of rays from a radiant
body, and an elastic reflector to control the said beam acted upon by sound
waves, and changed in form thereby to thus cause the direction of the rays
reflected therefrom to be changed, and their effect in a sensitive receiving body
to be varied in accordance with the said sound waves.
16th. In an instrument containing selenium as a portion of an electric circuit,
two pieces of conducting material insulated from one another, and provided with
a series of points near, but not in contact with one another, and selenium placed
between the said portions of conducting material at the said points to electrically
connect them, substantially as described.
17th. The herein described process of treating selenium, which consists in
raising its temperature until a structural change made apparent by an alteration
in the appearance of its surface as described, and by its increased electric con-
ductivity takes place, substantially as described.
18th. That improvement in the art or method of treating selenium, which
consists in heating the selenium to raise its temperature to the point at which
fusion begins, and allowing it to cool without fusion, all as and for the purpose
set forth.
19th. That improvement in the art or method of treating selenium, which
consists in applying heat thereto in an apparatus in which the selenium is visible
to the operator, to thereby enable the said operator to observe any changes
in the selenium that are made manifest in the external appearance thereof,
substantially as described.
20th. In an instrument containing selenium as a portion of an electric circuit,
a series of electric conductors arranged to form a cell having a curved bounding
surface, and selenium interposed between the said conductors at the said curved
surface to complete the electric circuit, substantially as described.
21st. In an instrument containing selenium as a portion of an electric circuit,
a series of electrically conductive discs and dises of insulating material to separate
them, of slightly smaller diameter than the adjoining conducting discs, and
selenium in the annular channels surrounding the periphery of the insulating
disc to connect the conducting discs, substantially as described.
22nd. In an instrument to interpose selenium in an electric circuit, a series of
electrically conductive discs and insulating discs of smaller diameter to separate
them, and selenium to connect them at their edges combined with electrical
connectors arranged to connect the alternate conductors discs together in one set,
and the remaining interposed connecting discs as another set, substantially as
described.
23rd. A selenium cell composed of plates of conducting material separated by
plates of insulating material, and connected at their edges by selenium, all the said
plates being provided with holes arranged in line to form a continuous passage
through the entire cell, the holes in the alternate conducting plates in one line
being larger than those in the interposed conducting plates in the same line,
which are all uniform in size combined with a conductor of the same size with and
inserted in the small holes, to electrically connect together all the plates having.
the small holes without forming electrical contact with those baving large the
holes, substantially as described.
24th. In a selenium cell, a series of conducting and insulating plates provided with
boles of different size arranged in line as described, to form a passage through the
cell combined with electric conducting material, inserted in the said passage in a
•

page_text: liquid or granular condition, and washers placed within the large holes, whereby'
the conducting plates containing the small holes are electrically connected by the
inserted conducting material, and the said conducting material is provented from
making electrical contact with the plates containing the large holes, substantially as
described.
In witness whereof, I, the said William Morgan-Brown, have hereunto set my
hand and seal, this Twenty fourth day of March, in the year of our
Lord One thousand eight hundred and eighty one.
W. MORGAN-BROWN. (L.S.)