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XL VIII. The Influence of Friction upon the Generation of a 

 Voltaic Current. By Shelford Bid well, M.A* 



IN ' Nature ' of March 4th Prof. Barrett calls attention to 

 the fact (which I believe had been observed before) that 

 the electro-motograph, or receiving-instrument of Edison's 

 loud-speaking telephone, is capable of generating an electric 

 current. He considers that we have here a new source of 

 electricity, the current generated being due to the motion of 

 a chalk cylinder under a metallic surface. His chalk, he adds 

 in a note, had been impregnated some months before with a 

 solution of phosphate of soda, but was, when used, practically 

 dry. 



The construction of the motograph is essentially as fol- 

 lows : — One end of an arm of brass is joined to the diaphragm 

 of the instrument ; the other end, which is faced with platinum, 

 is pressed by a spring against the upper surface of a horizontal 

 chalk cylinder. This cylinder is mounted on a thick brass 

 core or spindle, and can be made to rotate and rub against 

 the platinum on the arm by turning a winch-handle. The 



Diaphragm, z 



Brass arm. 



Platinum. 



Brass core. 



Chalk cylinder. 



cylinder is impregnated with certain chemical substances, of 

 which I believe caustic potash is always one, though it is not 

 mentioned by Prof. Barrett. 



It will be seen that there are here two metals, brass and 

 platinum, connected by a medium containing caustic potash ; 

 and the arrangement looks so much like a voltaic couple that 

 I was not surprised, on connecting the brass and platinum to 

 a galvanometer, to find a small + current flowing from the 

 platinum-faced arm. The cylinder was not rotated, and had 

 not been moistened for some months. On turning the handle 

 the galvanometer at once indicated a much stronger + cur- 

 * Kead before the Physical Society, March 13, 1880. 



