The Birmingham age-herald. [volume] (Birmingham, Ala.) 1902-1950, 1919-09-21

ular to the strips by the operation OF
diaphragm to which it is rigidly at
tached and on which speech sounds fall.
The movements of the diaphragm may
be expected, therefore, to control the OBJ
struction to the beam of light in such a
way that the intensity of the mergeant
beam varies in accordance with the
speech sounds. The practical objection
to this device is that ordinarily the move
ments of the diaphragm are so small that
it would be most difficult, II not impos-
sible, to make grids at once so light, so
rigid and SO fine as to fulfill the neces-
sary conditions Graham Bell does not, in
fact. claim that this method has been
actually used.
Ills second device is much more sound
from practical point of view. 1t relies
upon the fact that vibrating diaphragm
is continually, altering it's curvature con-
sequently if polished and interposed in a
steady beam of light it will give rise to
a reflected beam which is of variable
divergence. Although the total amount
of light reflected is actually unaltered,
the fraction of 1t incident at a distance
upon receiver, not large enough to in
clude the whole beam, will have a value
controlled by the vibrations Of the dia-
phragm. The objection in this case is
| that, of necessity, the diaphragm must
be large in order to deal with large
quantity of light for if 1t is placed at
| point where the beam has been con-
centrated to focus, the effect of. its
changes of curvature upon the diver
gence of the beam is negligible. Further
| from an acoustical point of view it would
be necessary for the diaphragm to be thin
, and 1t would, therefore, not be suitable
4. do faft v~zfx ~
teal properties
"In this apparatus" says DR.. Ran
kline, describing his own invention, the
essential point is the substitution of the
image of a grTN for the material grid
itself. This substitution at once sur
| mounts all the difficulties inherent in
! Graham Bells first proposal. 1t is no
longer necessary to attempt to construct
diminutive grids suitable for being
mounted upon and operated by speech
receiving diaphragms. Both grids are
now fixed in position and may be prac-
tically any size. 1t is the image of the
first grid which is caused by the in
cident speech to move to and fro with re-
spect to the second grid. The image Of
the first grid, in moving TO and fro over
the second grid, in effect opens and
closes shutter in the path of the BEAM"
SOUND MAGNIFIED
A curious effect may be obtained by
speaking loudly. If the voice is not mod
formed into screech. -Four and
five" for example, should be spoken
comparatively softly. 1.-TWO" and three"
need to be said more loudly.
A special reflector is set UP for use
with the sunlight. It is plane mirror
of nine inches diameter. 1t projects the
light through a water cell to remove most
pf Ia a ra
through a lens and the first grid and
focuses on the oscillating mirror on the
sound box. The trumpet, by the way,
is made Of thick drawing paper. 1t was
found much superior to tin which gives
too metallic a sound.
Interesting possibilities of development
are suggested. One is the substitution
of one of the grids by plane-convex
lens with the flat face silvered in paral
lei strips like grid. This lens thus be-
comes the grid and replaces the two used
in the present apparatus. The mirror on
the sound box reflects real image Of
the silvered grid upon the grid itself An
other possibility is substitute for the
gramaphone sound box by which with
telephone receiver and a transformer the
speaker may be in a separate room. This
has been tried, but it results in reduced
articulation.
What is the brilliancy Of the sun? In
England it is much less, of course, than
in the tropics. Still it is interesting to
note the result of experiments made with
the sunphone. Its value, compared with
''pointolite lamp is as $50 to 1.
To sum up results this is DR.. Rankine's
report: '"There appears to be very little
doubt that If selenium cells can be pro-
+, duced which are either more rapid in
action or free from internittency of con-
duction except when induced by light
fluctuations the transmission of speech
by light will be much facilitated. If both
these improvements can be effected even
a comparatively feeble source would prob
ably be capable of transmitting many
miles,
Already the ranges which have been
obtained are quite considerable. With