On the Suppression of Induction clamour in Telephones. 287 
A Fig. 9. 
B 
ments, and the two portions made to arrive at the opposite 
mouthpiece B a semi-undulation apart, so that interference occurs, 
and the sound is extinguished. One mouthpiece was fitted to the 
telephone, and the ear placed at the other, but, though by proper 
adjustment the musical note was almost obliterated, yet there 
remained a multitude of noises which were as bad as the original 
disturbance. The same objection applied to another arrangement 
I tried, in which inclination of a musical note is produced on the 
principle described by Lord Rayleigh.* Here (Fig. 10) the 
Fig. 10. 
length of the tube C is adjusted by a piston till it responds to a 
note entering at A, whereupon the ear placed at B hears no 
sound, energy of the sound-wave being wholly expended in set- 
ting the air at C into motion. 
Although, so far, these latter experiments are more or less un- 
successful, their publication may stimulate others to work, and it 
is quite possible that greater success may be obtained by ex- 
periments with the new loud-speaking telephone which has lately 
been devised, but which has not yet reached this country (June, 
1879). 
The hope expressed in the last paragraph has already received 
some fulfilment, for in a letter received to-day (June 16th), from 
* Sound, p. 196. 
