INFLUENCE OF THE USE OF THE TELEPHONE 
UPON THE HEARING BOWER.1 
By CLARENCE J. BLAKE, M.D., Boston. 
THE assertion made by the writer several years since, 
that the habitual use of the telephone would be preju- 
dicial to the hearing in many cases where the hearing was 
already impaired, was based upon the well-known facts of 
the process of accommodation in the middle ear for the 
transmission of tones of low intensity, of the susceptibility 
of the percipient apparatus to shock from sharp sounds of 
high intensity under the conditions of that process, and 
upon the results of measurements of the vibrations of tele- 
phone discs made for the purpose of determining approxi- 
matively the loss of power between the transmitting and 
receiving telephones. These experiments, the results of 
which were embodied in a paper read before the British 
Society of Telegraph Engineers in London in 1878, con- 
sisted in connecting two hand telephones, similar to those 
at present in general use, by means of flexible wires and 
recording the excursions of the discs of both the transmit- 
ting and receiving telephones by means of fine platinum 
wires tracing upon smoked glass. The excursion of the 
transmitting telephone disc without the magnet was first 
recorded, the average for' all the readings for a constant 
tone of 448 vibrations measured under the microscope, with 
micrometer eye-piece being 0.2625 millimetre. The deflec- 
tion of the centre of the disc under magnetic attraction was 
0.061 millimetre, the result of this being a decrease of the 
1 Read before the Am. Otological Society, Washington, September, 1888. 
Reprinted from the Archives of Otology, Vol. xvii., No. 3, 1888. 241 
Influence of the Telephone upon the Hearing Power. 
excursion in response to the same tone to 0.180 millimetre, 
a difference in the length of the excursion of 0.0725 milli- 
metre, or about 27.65 per cent. 
The movement of the receiving disc, as recorded on the 
smoked glass, was so slight that a large number of tracings 
was made, the average of which was, however, always 
within 0.02 millimetre, and controlling tests were made by 
means of a micrometer screw, reading to one-thousandth of 
a millimetre, connected with a delicate galvanometer, the 
results gained confirming the previous measurements of the 
transmitting disc and determining the average excursion of 
the receiving disc at 0.0135 millimetre, a loss in motion of 
p2.p per cent, between the two telephone discs. This loss 
of intensity is in a measure compensated for by the effort 
made in the ear itself to accommodate itself to the trans- 
mission of tones of low intensity, which effort, in its prime 
degree, can be maintained, as shown by experiment, for 
little more than fifteen seconds, at the end of which time 
the symptoms of fatigue (in a decrement of the hearing) 
begin to appear. Under this condition the ear is peculiarly 
susceptible also to the shock of such sharp metallic sounds as 
are constantly occuring in the practical use of the telephone. 
Estimating the amount of power in sound transmitted to 
the ear from the receiving telephone as but 7.1 per cent, of 
that which actuates the transmitting disc, the compensation 
required of the ear would seem to be considerable, particu- 
larly when it must be sustained fora long period, but when 
the attempt to estimate the percentage of the loss of the 
difference between consonant sounds of nearly the same 
logographic value, and consonant sounds, moreover, the 
pneumatic value of which results in a damping of the trans- 
mitting disc-by driving it further toward the magnet,-it 
is infinitely greater. 
Soon after the experiments above mentioned were made, 
the microphone transmitter, using a battery current, came 
into general use, and it seemed advisable to review the sub- 
ject in the light of experiments more delicate and more 
accurate than the crude measurements made ten years ago. 
For the results which follow I am indebted to Prof. W. Clarence J. Blake. 
242 
W. Jaques, of the American Bell Telephone Company, who, 
connecting a Blake transmitter with a hand telephone by a 
wire circuit, and comparing the values between sound aerially 
and telephonically transmitted, as measured by the distance 
from the ear, came to the conclusion that the speech given 
out by the receiver on a short line is approximately one 
ten-thousandth of the loudness of that going into the 
transmitter.' 
By a still later series of experiments the extent of the 
accommodative power of the ear, and correspondingly the 
demand made upon it, is still further illustrated. Connec- 
tion was made between the New York and Boston offices of 
the Telephone Company and the laboratory of the Massa- 
chusetts Institute of Technology in Boston, by means of a 
complete metallic (copper) circuit. The distance over this 
wire from the New York to the Boston office was 260 miles, 
and from the Boston office to the laboratory of the Institute, 
two miles. A Runnings transmitter was placed at each of 
these stations, and at the Institute of Technology; an 
electro-dynamometer was also included in the circuit. 
On speaking into the transmitter at the Institute, the 
electro-dynamometer gave a deflection of 22. mill6 amperes, 
speaking into the transmitter at the Boston office the cur- 
rent was 0.48 milld amperes, and speaking at New York it 
was 0.02 mill6 amperes ; the current was thus eleven hun- 
dred times as strong from the transmitter at the Institute 
as from that in New York ; and yet the conversation was 
1 " Taking D as the aerial and d as the telephonic transmission, the squares 
of the distances D and d should give an approximate measure of the loudness 
of speech going into the transmitter (T) and coming out of the receiver (R) : 
D2 
-^5- = E = the efficiency of the system or the relation of the sound emitted to 
that extent. 
" The mean of the first series of experiments was 
" D = 240 in. 
d = 2.5 in. 
E = .00011 
" The meant of a second series was 
" D = 360" 
d = 3.2" 
E = .00009 
" With two hand telephones, one as a transmitter, the other as a receiver : 
" D = 360 in. 
d = 0.8 in. 
E = .000005 
" Under a microscope, the movement of one electrode of a transmitter rela- 
tive to the other was .00025 >n-> and the movement of the receiver disc was 
.000005 in. or less."-Extract from letter dated Boston, Nov. 14, 1887. 243 
Influence of the Telephone upon the Hearing Power. 
distinctly audible in both cases, and the ear did not recog- 
nize any enormous difference in the intensity of the sound.' 
These facts so amply confirm the previous statements 
that they should be well borne in mind, especially since 
the telephone is an instrument the use of which will, in the 
future, increase rather than diminish, and since it is, more- 
over, not likely, with our present knowledge, to be essen- 
tially improved, the principal gains in clearness and 
distinctness of sound transmitted having to come from 
improvements in the means of communication rather than 
from changes made in the receiving instrument itself. All 
attempts at damping the high metallic overtones and im- 
proving the qualitative distinction between the consonant 
sounds as heard, by changing the structure of the receiving 
telephone, having resulted in a corresponding loss of that 
intensity, of which, as has been shown, there is so little to 
spare. 
1 Extract from letter dated Boston, June 20, 1888.