628 
Proceedings of the Royal Society 
convolutions were in contact, I failed to hear any sound ; but when 
I put two or three convolutions together and held them to the ear, 
the sound was again heard. I now isolated one convolution, and 
tied the thread of a paper telephone to it, and, although there 
was no neighbouring convolution in contact, I heard, by means 
of the telephone, the ticking distinctly, and, when the spiral was 
drawn out into a plain wire, the same sound continued. The cur- 
rent, as indicated by a tangent galvanometer of a single hoop of 
stout copper rod, produced a deflection of 54° for the unbroken cur- 
rent, and of 41° for the intermittent one. The cell resistance was 
under two ohms, and the exterior resistance under one ohm. The 
nitric acid was old, and had been frequently used. Removing the 
’04 wire from the circuit, and substituting a short length of *024 
copper wire, the current interruptions were heard still better in the 
paper telephone. I suspected mechanical transmission of the sound, 
but that could scarcely be, the wires being led from the open air by 
a fixed course under the floor. When all mechanical connection 
was broken through mercury troughs, there was no alteration ; and 
when a loop of 2 inches of *024 wire was held firmly in a vice it 
did not cease to sound. I need not, however, have been so scepti- 
cal, for sounds of a similar origin had been got as early as 1845 by 
Beatson, De la Rive, and other observers. They may not, without 
the aid of the mechanical telephone, have got in the wires the same 
clearly rendered series of ticks that we hear by its aid. De la 
Rive’s description of them, however, is both definite and graphic.* 
* His words are : — “Quant au son lui-meme, je ne peux pas mieux en donner 
une idee, qu’en le comparant a celui qu’on produit avec la roue de Savart. 
C’est une suite de bruits resultants du choc des particules metalliques les unes 
contre les autres, beaucoup plus qu’un son musical. On entend aussi, il est 
vrai, des sons musicaux. Ce sont les harmoniques du son que rendrait la tige 
ou le fil par l’effet des vibrations transversales; ils proviennent du mouvement 
vibratoire qu’eprouve le metal, mais ne sont pas un effet direct de l’influence 
electrique a laquelle il est soumis. On peut en effet, les faire dispar&itre en 
touchant avec la main le corps vibrant, sansque pour cela disparaisse le bruit 
f ondamental. ” — “Le son que rend un fil de fer bien recuit quand il transmet 
le courant est un son tres fort, qui ressemble beaucoup au son des cloches 
d’eglise dans le lointain. On pourrait peut-etre l’employer avec avantage dans 
les telegraphes electriques. ” — “ Le ton du son varie avec la vitesse avec laquelle 
les courants discontinus se succedent ; quand cette succession est tres rapide, le 
son ressemble beaucoup au bruit que fait le vent lorsqu’il souffle fortement.” — 
Covip. Rend . , 1845. 
