OF ARTS AND SCIENCES. 9 



into water included in tlie circuit. A sound proceeded from the distant 

 telephone. When two tuning-forks of different pitch were connected 

 together, and simultaneously caused to vibrate in the water, two musical 

 notes (the unisons respectively of those produced by the forks) were 

 emitted simultaneously by the telephone. 



A platinum wire attached to a stretched membrane, completed a 

 voltaic circuit l)y dipping into water. Upon speaking to the membrane, 

 articulate sounds proceeded from the telephone in the distant room. 

 The sounds produced by the telephone became louder when dilute sul- 

 phuric acid, or a saturated solution of salt, was substituted for the 

 water. Au'lible effects were also produced by the vibration of plumbago 

 in mercury, in a solution of bichromate of potash, in salt and water, in 

 dilute sulphuric acid, and in pure water. 



14. Sullivan * discovered that a current of electricity is generated 

 by the vibration of a wire composed partly of one metal and partly of 

 another ; and it is probable that electrical undulations were caused by 

 the vibration. The current was produced so long as the wire emitted 

 a musical note, but stopped immediately upon the cessation of the 

 sound. 



15. Although sounds proceed from the armatures of electro-magnets 

 under the influence of uiidulatory currents of electricity, I have been un- 

 able to detect any audible effects due to the electro- magnets themselves. 

 An undulatory current was passed through the coils of an electro- 

 magnet which was held closely against the ear. No sound was per- 

 ceived until a piece of iron or steel was presented to the pole of the 

 magnet. No sounds either were observed when the undulatory cur- 

 rent was passed through iron, steel, retort-carl)on, or plumbago. In 

 these respects an undulatory current is curiously different from an inter- 

 mittent one. (See par. 2.) 



16. The telephonic effects described above are produced by three 

 distinct varieties of currents, which I term respectively intermittent, 

 pulsatory, and undulatory. Intermittent currents are characterized by 

 the alternate presence and absence of electricity upon the circuit ; 

 Pulsatory currents result from sudden or instantaneous changes in the 

 intensity of a continuous current ; and undulatory currents are pro- 

 duced by gradual changes in the intensity of a current analogous to 

 the changes in the density of air occasioned by simi)le jiendulous 

 vibrations. The varying intensity of an undulatory current can be 



* Sullivan. " Currents of Electricity produced by the vibration of Metals." 

 Phil. Mag., 1845, p. 201; Arch, de I'^lectr., X., p. 480. 



