OF ARTS AND SCIENCES. 6 



and the sudtlen cessation of such attraction when the current is inter- 

 rupted. When a spiral of fine wire is made to dip into a cup of mer- 

 cury, so as thereby to close a galvanic circuit, it is well known that 

 the spiral coils up and shortens. Ferguson * constructed a rheotome 

 upon this principle. The shortening of the spiral lifted the end of the 

 wire out of the mercury, thus opening the circuit, and the weight of 

 the wire sufficed to bring the end down again, — so that the spiral was 

 thrown into continuous vibration. I conceive that a somewhat similar 

 motion is occasioned in a helix of wire by the passage of a discontinu- 

 ous current, although further research has convinced me that other 

 causes also conspire to produce the effect noted above. The extra 

 currents occasioned by the induction of the voltaic current upon itself 

 in the coils of the helix no doubt play an important part in the pro- 

 duction of the sound, as very curious audible effects are produced by 

 electrical impulses of high tension. It is probable, too, that a molecular 

 vibration is occasioned in the conducting wire, as sounds are emitted 

 by many substances when a discontinuous current is passed through 

 them. Very distinct sounds proceed from straight pieces of iron, 

 steel, retort-carbon, and plumbago. I believe that I have also obtained 

 audible effects from thin platinum and German-silver wires, and from 

 mercury contained in a narrow groove about four feet long. In these 

 cases, however, the sounds were so faint and outside noises so loud that 

 the experiments require verification. "Well-marked sounds proceed 

 from conductors of all kinds when formed into spirals or helices. I 

 find that De la Rive had noticed the production of sound from iron 

 and steel during the passage of an intermittent current, although he 

 failed to obtain audible results from other substances. In order that 

 such effects should be observed, extreme quietness is necessary. The 

 rheotome itself is a great source of annoyance, as it always produces 

 a sound of similar pitch to the one which it is desired to hear. It 

 is absolutely requisite that it should be placed out of earshot of the 

 observer, and at such a distance as to exclude the possibility of sounds 

 being mechanically conducted along the wire. 



3. Very striking audible effects can be produced upon a short circuit by 

 means of two Grove elements. I had a helix of insulated copper-wire 

 (No. 23) constructed, having a resistance of about twelve ohms. It 

 was placed in circuit with a rheotome which interrupted the current 

 one hundred times per second. Upon placing the helix to my ear I 



* Ferguson. Proceedings of Royal Scottish See. of Arts, April 9, 18G6; 

 Paper on "A New Current Interrupter." 



