362 Prof. Hughes on the Action of Sonorous Vibrations [May 9, 



May 9, 1878. 



Sir JOSEPH HOOKER, K.C.S.I., President, in the Chair. 



The Presents received were laid on the table and thanks ordered for 

 them. 



The following Papers were read : — 



I. " On the Action of Sonorous Vibrations in varying the Force 

 of an Electric Current." By Professor D. E. Hughes. 

 Communicated by Professor Huxley, Sec. R.S. Received 

 May 8, 1878. 



The introduction of the telephone has tended to develop our know- 

 ledge of acoustics with great rapidity. It offers to us an instrument 

 of great delicacy for further research into the mysteries of acoustic 

 phenomena. It detects the presence of currents of electricity that 

 have hitherto only been suspected, and it shows variations in the 

 strengths of currents which no other instrument has ever indicated. 



It has led me to investigate the effect of sonorous vibrations upon 

 the electrical behaviour of matter. Willoughby Smith has shown 

 that the resistance of selenium is affected by light, and Bornstein has 

 led us to believe that many other bodies are similarly affected. We 

 know also that the resistance of all bodies is materially influenced by 

 heat. Sir William Thomson and others have shown that the resist- 

 ance to the passage of currents offered by wires is affected by their 

 being placed under strains, and, inasmuch as the conveyance of 

 sonorous vibrations induces rapid variations in the strains at different 

 points of a wire, I believed that the wire would vary in its resistance 

 when it was used to convey sound. To investigate this I made a 

 rough-and-ready telephone, with a small bar magnet four inches long, 

 half the coil of an ordinary electro-magnet, and a square piece of 

 ferro-type iron, three inches square, clamped rigidly in front of one 

 pole of the magnet between two pieces of board. When using the 

 pendulum beats of a small French clock, or the voice, as a source of 

 sound, I found this arrangement supplied me with an extremely deli- 

 cate phonoscope or sound detector. 



All the experiments detailed in this paper were made with the 

 simplest possible means, and no apparatus of any kind constructed by 

 a scientific instrument maker was employed. The battery was a simple 

 Daniell's cell, of Minotto's form, made by using three common 

 tumblers, a spiral piece of copper wire being placed at the bottom of 

 each glass and covered with sulphate of copper, and the glass being 



