XL.—NOTES FROM THE PHYSICAL LABORATORY OF 
THE ROYAL COLLEGE OF SCIENCE FOR IRELAND: 
By W. F. BARRETT, Proressor or Puysics, Royan CoLLEGE 
OF SCIENCE, IRELAND, 
[Read February 17th, 1879. ] 
ON THE USE OF THE TELEPHONE AS AN INSTRUMENT 
OF PRECISION. 
It is well known that the Bell telephone forms a very sensitive 
galvanoscope. Ina paper read before the Royal Dublin Society, - 
on November 19, 1877, the present writer remarked :—“ The 
telephone reveals the existence of very feeble electric currents by 
the audible vibration of its iron disc. So prompt and sensitive 
is it to the slightest fluctuation in the strength of the currents 
traversing its coil, that it is not unlikely it may be of use in 
searching out rapid and feeble variations in a current that may 
escape detection by a galvanometer, owing to the inertia of even 
a light magnetic needle.” 
This application of the telephone is so obvious that it has, 
doubtless, occurred tovery many ; but Professor George Forbes was, 
I believe, the first practically to apply the telephone as an instru- 
ment of research. In a note published in “ Nature” (February 28, 
1878), entitled the “Telephone as an Instrument of Precision,” 
Professor Forbes points out that the feeblest thermo-electric cur- 
rents can be detected by the telephone. Drawing a hot copper 
wire along a rasp a hoarse croaking noise was heard in the at- 
tached telephone, proving the thermo currents set up. Next, using 
“a rasp-simply as an interruptor of the current, and employing a 
thermo-electric pile, Professor Forbes showed that a current which 
gave ‘a scarcely perceptible indication on a delicate mirror 
galvanometer was easily detected by the sound created in the 
telephone. Professor Forbes suggests that the telephone may be 
.of use in rapid signalling through submarine cables, by using 
interrupted currents at one end and a telephone at the other. 
Quite recently another inquirer, Mr. Blythe, writing in evident 
ignorance of Professor Forbes’s note, has brought under the 
