COLLECTION. CONCENTRATION, AND TRANSMISSION OF SOUND. SO AS TO FACILITATE THE HEARING THEREOF
Year: 1861

page_text: COLLECTION. CONCENTRATION, AND TRANSMISSION OF SOUND. SO AS TO FACILITATE
THE HEARING THEREOF."
Sealed the 10th December 1861, and dated the 19th October 1861.
PROVISIONAL SPECIFICATION left by the said John Marshall at the
Office of the Commissioners of Patents, with his Petition, on the 19th
October 1861.
I, JOHN MARSHALL, of No. 10, Savile Row, St. James', Westminster, in the
County of Middlesex, do hereby declare the nature of the said Invention for
"THE COLLECTION, CONCENTRATION, AND TRANSMISSION OF SOUND, 80 AS TO
FACILITATE THE HEARING THEREOF," to be as follows:-
I employ an apparatus consisting of two distinct reflectors adjusted together
in a manner to be hereafter described, and of an attached conducting tube.
First, I employ an external larger reflector, having a concave curved surface, on
which the sound is received and reflected towards a common focus. The
curvature of the surface of this first reflector may be that of a sphere, an
ellipsoid, a paraboloid, or an hyperboloid, or it may be of any other suitable
form; or I sometimes employ a combination of any such differently curved
surfaces, or the surface of the reflector may be conical, or of any other suitable

page_text: form. This first reflector serves to concentrate the sound, and I call it the
"concentrating reflector." Secondly, I employ an internal smaller reflector
adjusted in the axis of the larger one, to the focus of which its position has a
definite relation. It may be so arranged that by means of a screw or other
suitable contrivance its position within the axis of the concentrating reflector
may be adjusted or altered. The surface of this second or "axial reflector" is
so formed as to reflect the rays of the concentrated sound in parallel or nearly
parallel lines in a definite direction. This surface is either convex or concave,
or partly convex and partly concave, and has one curvature or another,
according to and dependent on the form of the first or concentrating reflector.
This second or axial reflector receives the concentrated sound reflected from
the concentrating reflector, and again reflects it so concentrated through an
opening in or near the middle of the concentrating reflector leading into a
conducting tube. Thirdly, this conducting tube is attached at one end to
the convex or outer surface of the concentrating reflector, over the before-
mentioned central opening, and at its other end it is adapted to fit into
or upon the ear. Along this tube the concentrated sound is transmitted
to the ear. I sometimes form the tube at the end which is attached to
the concentrating reflector in such a manner as to constitute a second
smaller concentrating reflector, having also a second axial reflector, the effect
of which is precisely similar to that of the first, namely, the still further
concentration of the sound, and the transmission of the same in parallel
or nearly parallel lines; or I employ two or more such combinations of
reflectors placed one behind the other. I sometimes also form the interior
of the tube at the end of the same which fits into or upon the ear of a
parabolic or other suitably curved surface, so that it still further concentrates
the sound on its passage into the ear. With the view of further perfecting
the apparatus, the axial reflector may be made hollow, and perforated at its
vertex or summit, so as to transmit directly the rays of sound coming along or
near the axis. I propose to make the above-described apparatus of any size
and of any material I may find suitable for the special purpose for which it is
to be employed, and either to polish, groove, channel, engrave, electrotype,
japan, varnish, or otherwise finish or cover the reflecting and other surfaces.
I further propose to make this apparatus either in one piece or in several
pieces, capable of being separated and put together, or to fold together and
open out, so that it may be more easily carried or packed; and I likewise
propose to adapt it in any way I may select for the purpose of being used by
both ears at once, in which case the form of the apparatus may be somewhat
modified; and also to combine two or more apparatuses of the same kind to

page_text: receive sounds coming in different directions, and in some cases I provide one
apparatus with several conducting tubes.
The general purposes of my Invention are, first, to assist those persons
whose hearing is defective to hear better; and, secondly, to enable those whose
hearing is not defective to hear weak or distant sounds better, or even sounds
that are otherwise imperceptible.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said John Marshall in the Great Seal Patent Office on the 17th
April 1862.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
MARSHALL, of No. 10, Savile Row, St. James', Westminster, in the County of
Middlesex, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Nineteenth day of October, in the year of our Lord
One thousand eight hundred and sixty-one, in the twenty-fifth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said John Marshall, Her special licence that I, the said John Marshall, my
executors, administrators, and assigns, or such others as I, the said John
Marshall, my executors, administrators, and assigns, should at any time agree
with, and no others, from time to time and at all times thereafter during the
term therein expressed, should and lawfully might make, usc, exercise, and
vend, within the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for "THE COLLECTION, CONCENTRATION.
AND TRANSMISSION OF SOUND: 50 AS TO FACILITATE THE HEARING THEREOF," upon
the condition (amongst others) that I, the said John Marshall, my executors
or administrators, by an instrument in writing under my, or their, or one of
their hands and seals, should particularly describe and ascertain the nature of
the said Invention, and in what manner the same was to be performed, and
cause the same to be filed in the Great Seal Patent Office within six calendar
months next and immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said John Marshall, do hereby declare the
nature of the said Invention, and in what manner the same is to be performed,
to be particularly described and ascertained in and by the following statement
thereof, reference. being had to the accompanying Drawings, and to the figures
and letters marked thereon, that is to say:
I employ an apparatus consisting of two distinct reflectors adjusted together

page_text: in a manner to be hereafter described, and of an attached conducting tube.
First. I employ an external larger reflector having a concave curved surface,
on which the sound is received and reflected towards a common focus. The
curvature of the surface of this first reflector may be that of a sphere, an
ellipsoid, a paraboloid, or an hyperboloid, or the surface may be conical or of
any other suitable form, but by preference I make the curvature that of a
paraboloid for hearing distant sounds, and that of a portion of an ellipsoid for
hearing nearer sounds. I sometimes employ a combination of any such
differently curved surfaces. This first reflector serves to concentrate the
sound, and I call it the "concentrating reflector." Secondly, I employ an
internal smaller reflector adjusted in the axis of the larger one, to the focus of
which its position has a definite relation. This inner reflector, which I term
the axial reflector," may be so arranged that by means of a screw or other
suitable contrivance its position within the axis of the concentrating reflector
may be adjusted or altered, or it may be simply fixed by stays, or in any other
suitable manner to the concentrating reflector. The surface of the axial
reflector is so formed as to reflect the rays of the concentrated sound in
parallel or nearly parallel lines in a definite direction, and may be either
convex or concave, or partly convex and partly concave, and have one
curvature or another according to and dependent on the form of the con-
centrating reflector. This axial reflector receives the concentrated sound
reflected from the concentrating reflector, and again reflects it so concentrated
through an opening in the back of the concentrating reflector leading into a
conducting tube. Thirdly, the conducting tube is attached at one end to the
outer surface of the concentrating reflector over the before-mentioned opening,
and at its other end it is adapted to fit into or upon the ear. Along this tube
the concentrated sound is transmitted to the ear.. I sometimes form the tube
at the end which is attached to the concentrating reflector in such a manner
as to constitute a second smaller concentrating reflector, which may also be
provided with a second axial reflector, the effect of which is to still further
concentrate the sound, and transmit the same to the ear in parallel or nearly
parallel lines, or I employ three or more such combinations of reflectors. I
sometimes also form the interior of the tube at the end which fits into or
upon the ear of a parabolic or other suitably curved surface, so that it still
further concentrates the sound on its passage into the ear; and when the tube
is formed with a bend for the more convenient use of the instrument, I prefer
to cut off the angle of the bend, and replace it by a flat or slightly curved
surface acting as a reflector, by which the sound is transmitted in a more
perfect manner through the bend. With a view of further perfecting the

page_text: apparatus the axial reflector may be made hollow; and perforated at its vertex
or summit, so as to transmit directly the rays of sound coming along or near
the axis of the instrument. I propose to make the above-described apparatus
of, any size and of any material I may find suitable for the special purpose for
which it is to be employed, and either to polish, groove, channel, engrave;
electrotype, japan, varnish, or otherwise finish or cover the reflecting and other
surfaces. I further propose to make this apparatus either in one piece or in
several pieces, capable of being separated and put together; or to fold together
and open out, so that it may be more easily carried or packed; and I-likewise
propose to adapt it in any way I may select for the purpose of being used by
both ears at once, in which case the form of the apparatus may be somewhat
modified; and also to combine two or more apparatus of the same kind to
receive sounds coming in different directions, and in some cases I provide one
apparatus with several conducting tubes.
The general purposes of my Invention are, firstly, to assist those persons
whose hearing is defective to hear better; and, secondly, to enable those whose
hearing is not defective to hear weak or distant sounds better, or even sounds
that are otherwise imperceptible.
But in order that my Invention may be more easily understood and readily
carried into effect, I will now describe the best means I am acquainted with
of performing the same.
Figures 1, 2, and 3, on Sheet I. of the accompanying Drawings, shew the
construction of my improved apparatus which I prefer to adopt for facilitating
the hearing of distant sounds. Figure 1 shews a longitudinal section through
the apparatus, Figure 2 shews an end view of the same, and Figure 3 shews
the method which I prefer to employ for obtaining the form of the concen-
trating reflector. Similar letters of reference indicate similar parts in all the
Figures. The form of the concentrating reflector a is in this case that of a
paraboloid, for the reason that rays of sound coming from a distance may be
assumed to travel in parallel or nearly parallel lines, and that it is the pro-
perty of the parabolic curve to cause all rays which proceed in a direction
parallel to its axis and strike upon its inner surface to be reflected to its focus.
The principle upon which I prefer to construct this form of the concentrating
reflector is as follows:-Upon the base line b, Figure 3, representing the
diameter of the reflector at its mouth, I construct an equilateral triangle b, c, d,
of which the apex e represents the focus of the parabolic curve a. A line f,"
drawn through the apex e perpendicularly to the base b, will then constitute the
axis of the parabola. By setting off upon this line from the point the
length of the side of the equilateral triangle b, c, d, a point will be obtained,

page_text: and by bisecting the distance between h and e, I obtain the point i, which is the
apex of the parabolic curve a. If upon the sides c and d of the triangle any
number of optional lengths e w, ex, ey, ez, are set off from the point e, and the
same lengths w¹, hx. hy', h z¹, are set off upon the line from the point h, then
by drawing perpendicular lines from the points w¹, x, y, z¹, and striking arcs
from the centre e through the points w, x, y, z, points of intersection,
, 22, will be obtained, which constitute so many points in the parabolic
curve a. Any other mode of constructing the parabolic curve may be
employed, as I have only given the one herein-before described on account of
its simplicity. I obtain the size and position of the opening u in the end of
the concentrating reflector a by cutting off so much of the paraboloid as lies
beyond a plane vertical to the axis f, and passing through the focus e. The
axial reflector is also constructed of a paraboloidal form, the length from
its focus to the extreme point being by preference rather less than the cor-
responding dimensions of the concentrating reflector a; its extreme diameter v
is equal to two-thirds of the diameter of the aperture in the reflector a,
and it is by preference so adjusted in the axis of the latter that its focus
corresponds in position with the focus of the reflector a. It is held in this
position by means of stays 1, 1, fixed to it and to the reflector a, or in any other
suitable manner.
I do not limit myself either to the exact proportions or forms of the
reflectors a and k, nor to their precise relative adjustment, as herein-before
described, as other proportions and relative positions may be adopted, affording,
however, less accurate results.
The conducting tube m is attached to the opening u of the reflector a, and
may be made either conical or slightly paraboloidal in form, its length being
optional; it is provided with an ear piece n of any suitable form to fit into or
upon the ear, and it may be either straight, as shewn, or curved, or bent; but
in the latter case I prefer to provide it in the bend with an angle reflector, to
be hereafter described.
By the before-described combination of the two reflectors a and k, it will be
seen that any rays of sound 1, 2, 3, travelling in parallel lines, and striking
upon the inner surface of the concentrating reflector a, will, by virtue of the
well-known property of the parabolic curve, all be reflected towards the
focus e, and striking upon the outer surface of the axial reflector k, which sur-
rounds this focus, will be further reflected by the same in parallel lines in the
direction of the conducting tube m. Any other rays of sound 4, 5, that do
not proceed in a direction parallel with the axis of the apparatus, and that
strike upon the front portion of the axial reflector k, will also be reflected by

page_text: the same in a parallel or nearly parallel manner down the conducting tube.
It will be readily understood that the loudness of sound being increased by
the concentration of the rays, and its clearness being augmented by projecting
the rays so concentrated in parallel lines on to the tympanum of the ear, the
greatest available power of magnifying sound in a perfectly distinct manner is
attained by the use of this apparatus.
Figures 4, 5, 6, shew the construction of my improved apparatus which I
prefer to adopt for facilitating the hearing of near sounds, particularly adapted
for persons of defective hearing. Figure 4 shews a longitudinal section,
Figure 5 shews an end view, and Figure 6 shews the method of construction
which I prefer to employ for obtaining the form of the concentrating
reflector a, which in this case is ellipsoidal, this form possessing the property
of causing all rays of sound proceeding from a point situated at the one focus
of the ellipsoid and striking upon its inner surface to be reflected to the
other focus.
The principle upon which I prefer to construct this concentrating reflector
is as follows: Upon a base line b, Figure 6, representing the diameter of the
reflector at its mouth, I construct an equilateral triangle b, c, d, of which the
apex e represents one focus of the elliptic curve a. A line f, drawn through
the apex e perpendicularly to the side b, will then correspond with the position
of the long diameter of the ellipse.
Assuming in this instance that the apparatus is intended to convey to the
ear rays of sound proceeding from a point situated at a distance of two feet
from the focus of the reflector, which is about the distance at which con-
versation is carried on between two persons, I set off a distance of two feet
from the point e, and from the point g, which is the second focus of the elliptic
curve a, I draw a line g, h. The length of this line added to the length of
the side c of the equilateral triangle will give the long diameter of the ellipse,
and half the difference between this line and the focal distance e, g, carried
beyond the focus e, will give the apex of the elliptic curve a. Any number
of points in this curve may be obtained by the intersection of arcs struck
from each of the points e and gas centres with radii, the sum of each pair of
which is equal to the sum of the lines c and h, g. Although I have given the
above method for constructing the elliptic curve a, I do not confine myself to
the use of the same only, as any other method of construction may be
employed. The size and position of the opening u at the end of the concen-
trating reflector a is obtained by cutting off so much of the ellipsoid as lies
beyond a planej, Figure 6, laid through the focus e perpendicularly to the
axis f.
The axial reflector is in this case composed of three differently

page_text: formed surfaces. The portion ¹, which is intended to receive all the rays of
sound coming from the point g, and reflected by the surface of the concen-
trating reflector a, is formed paraboloidal. The portion, which is intended
to receive rays of sound proceeding from points in the axis f at distances
varying from two feet to eight inches from the focus of the instrument, is
formed with an approximating paraboloidal curvature. The focus of the
parabola, a portion of which is employed for generating this form, is deter-
mined by the point of intersection o of the reflected rays 1, proceeding from a
distance of eight inches to the extreme edge of the reflector a, and 2 pro-
ceeding from the same point to the back part of the reflector a. The diameter
at p of this portion of the axial reflector I prefer to make two-thirds of the
diameter of the opening w, and allow it to project forward to about three-
fifths of the length of the concentrating reflector a; the point of unison of the
two portions, and 2 of the axial reflector is determined by the point at
which the reflected rays 3, proceeding from the point g to the extreme edge h
of the reflector, strike the surface of k¹, as shewn by the dotted line r. The
portion of the paraboloid beyond the focus e is cut off, and the third
portion, which is conical, and serves to receive rays of sound proceeding
from a greater distance than two feet, is fixed to the end of k¹. This axial
reflector is connected to the concentrating reflector by means of stays 1, 1, or by
any other suitable means. I do not limit myself either to the exact propor-
tions or forms of the reflectors a and k, nor to their precise relative adjust-
ments, as herein-before described, as other proportions and relative positions
may be adopted, affording, however, less accurate results.
In some cases, and particularly for the use of very deaf people, I construct
my improved apparatus with a very small focal distance for the concentrating
reflector a, that is to say, with the external focus g, whence the rays of sound
proceed, in close proximity to the mouth of the reflector, so that it shall take
in the greatest possible number of rays proceeding from that point. Again,
in other cases I construct the apparatus with a greater focal distance than
that herein-before mentioned.
The tube m is attached to the opening u of the reflector a, and is formed
conical and of any convenient length. It may be either straight or with a
bend, as shewn, in which case I prefer to cut off the outer angle of the bend,
and replace it by a flat or slightly concave surface q acting as a reflector, by
which the rays of sound are conveyed through the bend in a more perfect
manner than would otherwise be the case. I prefer to make the part m¹ of
the bend of such a form as to be a continuation of the conical part m, and
provide it with a suitably formed ear piece n.

page_text: In some cases I form the conducting tube m in a telescopic manner, that is
to say, so that one portion of the tube can slide longitudinally inside another
portion of the same, by which arrangement the length of the tube can be
adjusted so as to bring more distant or nearer sounds properly into the focus
of the concentrating reflector. Or I sometimes form the part m³ to screw off
the ordinary length of tube m, and screw on to or insert into this latter an
extra length of tube, which may or may not be telescopic, and to the end of
this I again attach the angular piece m¹.
A great advantage in the before-described improved apparatuses is, that
the "buzz" or "roar" which occurs in instruments of present construction is
so diminished as not to be inconvenient to ordinarily deaf ears, and it may be
so entirely prevented as not to be perceptible to healthy ears, by leaving a
narrow circular spaces between the ear piece n and the tube m¹, upon which
it fits.
I sometimes connect several of the before-described concentrating reflectors
with their axial reflectors either of the paraboloidal or of the ellipsoidal form
to one and the same conducting tube, as shown in the back view at Figure 16,
and in longitudinal section on line x, x, at Figure 17, where three reflectors
a, a, a, with their axial reflectors k, k, k, have each separate conducting tubes
m, m, m, which converge and unite into one tube at m¹ having an ear piece n.
By this arrangement the sound is conducted from various quarters at once to
the ear.
In cases where a number of reflectors are connected in a similar
manner to one and the same conducting tube, I sometimes construct the con-
centrating reflectors so that the transverse section of each one is of an
hexagonal form, by which they are enabled to fit closely one against the other,
similar to the cells of a honeycomb; the axial reflectors are formed circular in
transverse section, as usual.
In Figure 7 is shewn a longitudinal section of a possible arrangement of
my apparatus, in which the concentrating reflector is composed of a paraboloidal
portion a and a spherical portion a', whilst the axial reflector consists of the
convex paraboloidal surface b, which serves to reflect the rays coming from
the portion a of the concentrating reflector and of the concave surface b¹, which
reflects the rays coming from the portion a' of the concentrating reflector;
such an arrangement would, however, act in an imperfect manner, owing to
the considerable interference of the reflected rays.
In Figure 8 is shewn a longitudinal section of an arrangement of my
improved apparatus, which may be adopted for large sized instruments. Here
the concentrating reflector a and axial reflector k are constructed similar to

page_text: those shewn in Figures 1 and 2; but in order still further to concentrate the
sound, a second concentrating reflector a¹, provided with a second axial
reflector k¹, is attached to the opening of the reflector a.
Figure 9 shows a longitudinal section of an arrangement of my improved
apparatus, wherein the axial reflector is capable of being adjusted in the
axis of the concentrating reflector a by means of a screw spindle b, to which
it is attached, and which passes through a fixed nut c, carried by means of
stays d, and is provided with a knob e for facility of adjustment. This
arrangement is applicable to very large. instruments, where in the expansion
or contraction of the material of which the two reflectors are composed may
be sufficient to derange the accurate relative adjustment of the same. The
reflector a is here shown attached to a stand f, which may be also applied to
any other of the before-described arrangements. The conducting tube m may
be rigid, as shown, or flexible, as indicated by the dotted lines at m¹; this
latter arrangement would, however, not be so advantageous, as the parallelism
of the rays would thereby, be somewhat disturbed.
The concentrating reflectors a, a,
side which fits against the face,
The axial reflectors k, k, relain
Figure 10 shews a front elevation, and Figure 11 shews a plan, of an
arrangement wherein two of my improved instruments are connected together
so as to fit one on each ear of a person.
have in this case a piece cut away from the
which piece is replaced by a flat surface b, b.
their ordinary form and position. The conducting tubes m, m, are here
shown very short, with angular reflectors c, c, as before described, for trans-
mitting the rays of sound through the bend; small discs d, d, are attached to
the tube to fit against the ear, and to these discs, or in any other convenient
manner, are attached the springs e, f, which hold the instrument to the head.
Instead of constructing the conducting tubes as shown, they may be made
longer and flexible, so as to pass round the back of the head to the opposite
ear.
Figure 12 shews an elevation, Figure 13 shows a plan, and Figure 14
shews a vertical section, of an arrangement of my improved apparatus adapted
for concentrating and conveying rays of sound proceeding from several
directions at once to the ear. For this purpose six of the before-described
combined concentrating reflectors a, a, a, and axial reflectors k, k, k, are here
shown arranged round and connected to a hollow tube or stem b, fitted at the
bottom with a stand c; any other convenient number of reflectors may, how-
ever, be employed. Opposite the opening of each concentrating reflector a is
fixed a flat sound reflector d, d, d, by which all the rays of sound projected

page_text: into the top of the tube are reflected in a parallel manner to the bottom of
tube b, where they are again received by an angle reflector e, which directs
them horizontally either into an ordinary conducting tube, or when the
apparatus is of large dimensions, another concentrating reflector f, with its
axial reflector g, may be fixed to the tube opposite the reflector 1, so as to con-
centrate still further all rays of sound proceeding from the same, and to
convey them so concentrated into the conducting tube h.
This apparatus might be applied with advantage on a large scale on a sea
shore for facilitating the hearing of signal guns from ships in distress, or in
any situation where it is desirable to hear accurately sounds proceeding from
all quarters, or it may be employed on a small scale for domestic purposes.
In some cases I provide several conducting tubes opposite the reflector e, so
as to permit of several persons making use of the apparatus' at the same
time; and when it is required to distinguish by the aid of this instrument the
quarter whence certain sounds proceed, I replace the single reflector e by
a number of reflectors corresponding in position to those at d, d, d, and fix a
conducting tube opposite each one, by which arrangement the sounds pro-
ceeding from a certain quarter, and collected by one particular reflector a,
will be conveyed to and heard most distinctly at the corresponding conducting
tube.
I sometimes employ an arrangement of my improved apparatus as shewn in
section in Figure 15, for conveying minute and almost imperceptible sounds
in the most concentrated manner possible to the ear; this arrangement is par-
ticularly adapted for scientific researches. For this purpose I construct the
concentrating reflector a of such an ellipsoidal form that the second focus e¹
of the generating ellipse is situated at or near the mouth of the reflector, as
shown, the axial reflector k being in paraboloidal, and arranged with its focus
corresponding in position with the other focus e of the concentrating reflector,
as herein-before described with reference to the other arrangements; then, if
the object from which the sound emanates be placed at the focus e¹ of the appa-
ratus, all rays of sound that proceed from the same and strike the inner surface
of the ellipsoid will be reflected towards the other focus e, where they will be
received in a concentrated form by the axial reflector k, and be reflected by
the same up the conducting tube m, as herein-before described with reference
to other arrangements. If it is desired to collect all possible rays of sound
emanating from the object, then a stand or table o may be constructed, as
shown in dotted lines, having a recess a¹ corresponding in form with that por-
tion of the ellipsoid which is situated beyond the focus e', with suitable

page_text: provision for holding the object in the focus e¹, so that on placing the apparatus
over the recess a³, nearly all the rays of sound proceeding from the object
under examination, and striking upon the surface of the recess, will be also
reflected on to the axial reflector. k.
In some cases I employ this form of my improved apparatus as a stetho-
scope, in which case I prefer to cut off the ellipsoid for forming the concen-
trating reflector at the small diameter x, and make the focal distance e, e¹, such
that half of the same, or the distance from x to e¹, shall be equal to the distance
of the organ to be examined from the surface of the human body. Instead of
forming the concentrating reflector of my improved apparatus of one continuous
curved surface, as herein-before described, I sometimes construct the same as
shown in longitudinal section at Figure 18, Sheet II., and in front view at
Figure 19, wherea¹, a, a, a, are concentric zones of paraboloidal surfaces,
each formed in such a manner and so arranged relatively one to the other that
focii of all the parabolic curves are situated at one and the same point e,
by which arrangement all the parallel rays of sound 1, 2, 3, 4, striking the
inner surface of each zone are as before reflected in a concentrated manner
to the common focus e, and are received by the axial reflector k, which reflects
them in a parallel manner into the conducting tube m. The width and diameter
of the outer zone being optional, I prefer to make the other zones a³, a³, a of
such diameters that the ray of sound which strikes the lowest point of a' shall
just clear the upper edge of a³, and so on for each succeeding zone, whilst
their widths are so proportioned that the reflected rays 1, 2, 3, from the ex-
treme outer edges of the reflectors a¹, a², a³, just clear the inner edges of the
reflectors a², a³, a', respectively. The inner zones a³, a³, a', may be connected
to the outer one a¹ by means of stays h, h, h, or in any other suitable manner,
and the zone a¹ may be connected to the conducting tube m by means of a
conically formed piece n, or by any other suitable contrivance that does not
interfere with the reflected rays of sound.
The same mode of constructing the concentrating reflector may also be
adopted for the ellipsoidal form, as shewn in longitudinal section in Figure 20,
where a¹, a³, a³, a', are concentric zones of ellipsoids, of all of which the focii
are situated respectively at e and e¹. The principle upon which I prefer to
regulate the relative diameters and widths of the zones is the same as described
in the preceding arrangement.
A certain amount of concentration of sound may be obtained by construct-
ing both the concentrating and axial reflectors of my improved apparatus of a
conical form, as shewn in longitudinal section in Figure 21, Sheet II., which

page_text: arrangement will, however, act in a very imperfect manner, as a considerable
amount of sound is intercepted by the axial reflector, and it is only correctly
applicable to parallel rays of sound.
In order to preserve the parallelism of the rays reflected from the axial
reflector k, the side of the same must be parallel to the side of the concentra-
ting reflector a. If the angle of the cone forming the axial reflector be
made greater than that of the cone forming the concentrating reflector a, then
the rays reflected from k into the conducting tube n will converge more or
less. Instead of forming the two reflectors a and k of a circular transverse
section, they may also be constructed of a polygonal form.
In Figures 22 and 23, Sheet II., is shown another possible modification of
my improved apparatus, by which the rays of sound would be to a certain
extent concentrated and projected into the conducting tube in a more or less
parallel manner. Figure 22 shews a longitudinal section on line 2, 2, and
Figure 23 shows a front view. The concentrating reflector a is here shewn of
a bell or trumpet shape; it may, however, be formed in a similar manner io
the reflectors of the first described arrangements. The axial reflector as
described with reference to the former arrangements is replaced by three or
more partitions k, k, k, dividing the concentrating reflector into a similar number
of compartments.
The central angles which these partitions would form by their intersection
are, by preference, gradually more and more rounded off towards the mouth of
the instrument, as shown, so as to form a description of pyramidal axial reilec-
tor, by which the concentrated rays of sound will be projected into the
conducting tube m, in a manner approaching nearer to parallelism than would
be the case if the partitions formed angles of intersection.
This latter arrangement, although affording very imperfect results as com-
pared with the previously described arrangements, may, however, be adopted
in cases where cheapness of the apparatus is a greater object than perfect accu-
racy of action.
Having now described the nature of my Invention, and in what manner the
same is to be performed, I wish it to be understood that I in no way limit myself
to the exact shape and arrangement of my improved apparatus as shown in the
various Figures on the accompanying Drawings, as numerous other modifica-
tions of the same may be employed, though with a less perfect result, without
departing from the nature of my Invention; but what I claim under the before
in part recited Letters Patent is, the construction of apparatuses for the collec-
tion, concentration, and transmission of sound, in which a combination of

page_text: reflecting surfaces is employed, which are so formed and are adjusted in such
relative positions that the rays of sound are received on one or more of these
reflecting surfaces, and are thence reflected in a concentrated níanner on to one
or more other reflecting surfaces, by which they are again reflected in a
parallel or nearly parallel manner, into a conducting tube or into several con-
ducting tubes, which conveys or convey them to the ear, substantially as herein-
before described with reference to the accompanying Drawings.
In witness whereof, I, the said John Marshall, have hereunto 'set my
hand and seal, this Fifteenth day of April, in the year of our Lord One
thousand eight hundred and sixty-two.
JOHN MARSHALL. (L.S.)