OF ARTS AND SCIENCES. 305 



carbon transmitter or microphone. Tie to the thread from a common 

 string telephone a nail or a screw two or three inches long, and let the 

 latter hang over one pole of the magnet while the ear is applied to the 

 open end of the tube. Let one at the transmitter talk, or make musical 

 sounds, and they will be heard while the nail or screw is slowly dragged 

 over the pole. The motion necessary for this is very small, two inches 

 a minute being quite sufficient to produce the maximum effect with 

 a magnet half an inch in diameter. ^ --" 



It is not essential, either, that the magnet should rotate, for if a 

 strip of paper is put between the magnet and the armature and slowly 

 pulled between them while the vibratory current passes, the sounds 

 will be heard as before. Also, the same is effected by letting the 

 armature project beyond the magnet, and rest upon a pulley of wood 

 or other substance, which may be rotated as in the other cases. 



With the instrument I exhibit I have heard talking at the distance 

 of a foot from the ear, and musical sounds anywhere in a room thirty 

 feet square, using a single bichromate cell and an Edison transmitter, 

 the current being probably about one tenth of a Weber. I have 

 named this instrument the rotaphone. 



vol. xiv. (n. s. vi.) 20 



