OP ARTS AND SCIENCES. 7 



circuit. I failed to obtain audible effects in tbis way when the pitch 

 of the rbeotome was high. Elisha Gray * has also produced audible 

 effects by the passage of induced electricity through the human body. 

 A musical note is occasioned by the spark of a Ruhmkorff's coil when 

 the primary circuit is made and broken sufficiently rapidly. When 

 two rheotomes of different pitch are caused simultaneously to open and 

 close the primary circuit, a double tone proceeds from the spark. 



9. AVhen a voltaic battery is common to two closed circuits, the 

 current is divided between them. If one of the circuits is rapidly 

 opened and closed, a pulsatory action of the current is occasioned upon 

 the other. 



All the audible effects resulting from the passage of an intermittent 

 current can also be produced, though in less degree, by means of a 

 pulsatory current. 



10. When a permanent magnet is caused to vibrate in front of the 

 pole of an electro-magnet, an undulatory or oscillatory current of 

 electricity is induced in the coils of the electro-magnet, and sounds 

 proceed from the armatures of other electro-magnets placed upon the 

 circuit. The telephonic receiver referred to above (par. 4), was con- 

 nected in circuit with a single-pole electro-magnet, no battery being 

 used. A steel tuning-fork which had been previously magnetized was 

 caused to vibrate in front of the pole of the electro-magnet. A 

 musical note similar in pitch to that produced by the tuning-fork 

 proceeded from the telephonic receiver in a distant room. 



11. The effect was much increased when a battery was included in 

 the circuit. In this case, the vibration of the permanent magnet threw 

 the battery-current into waves. A similar effect was produced by the 

 vibration of an unmagnetized tuning-fork in front of the electro-magnet. 

 The vibration of a soft iron armature, or of a small piece of steel spring 

 no larger than the pole of the electro-raagnet in front of which it was 

 placed, sufficed to produce audible effects in the distant room. 



12. Two sino-le-pole electro-magnets, each having a resistance of 

 ten ohms, were arranged upon a circuit with a battery of five carbon 

 elements. The total resistance of the circuit, exclusive of the battery, 

 was about twenty-five ohms. A drum-head of gold-beater's skin, 

 seven centimetres in diameter, was placed in front of each electro- 

 magnet, and a circular piece of clock-spring, one centimetre in 

 diameter, was glued to the middle of each membrane. The telephones 

 so constructed were placed in different rooms. One was retained in 



* Elisha Gray. Eng. Pat. Spec, No. 2646, see " Engineer," Aug. U, 1874. 



