266 A New Form of Influence- Machine. 



but then the charges alternate from positive to negative with 

 each half revolution of the disks. 



An approximate measure of the efficiency of the machine 

 is seen by the following experiments. 



The glass throughout was held free from electrical excite- 

 ment, and the disks were rotated sixty times per minute ; the 

 actuating cause was then removed, and the disks came to rest 

 after making forty-seven revolutions. This measures the 

 friction of the machine. 



The disks were then similarly turned, but the electrical 

 charges were allowed to collect ; it was then found that the 

 disks came to rest after twenty-three revolutions. The fric- 

 tion of the machine, therefore, is about equal to the repulsion 

 of the electrical charges. 



Leyden jars having eight square inches of tinfoil in each 

 coating were then connected to the terminals, and the ter- 

 minals set 3J in. apart : the disks were turned to the same 

 number of revolutions and then left to come to rest, which 

 they did after producing eighty sparks. 



The disks were then turned and the number of sparks 

 counted in relation to each revolution. This gave seven 

 sparks of 1 in. length, five of 2 in., four of 3 in., and three of 

 4 J in. length. 



Eight metal sectors were then added (total 112 square 

 inches on each disk) : with them the self-excitement becomes 

 so free that, before any circuit was made, presenting the 

 fingers to the disks caused electrical discharges. 



When the circuits are made between the several brushes 

 the disks appear to be seething with electricity, and the 

 charges shoot out for a considerable part of their circum- 

 ference, but chiefly at the top and the bottom, where they are 

 not covered by the vertical glass slips, for the change of the 

 charges from + to — takes place upon the disks just as they 

 pass the edge of the slip. Improvements in this respect 

 might be made, but the present arrangement has the ad- 

 vantage of giving permanence to the respective charges. 



It will be noticed that strips of tinfoil are placed over the 

 receding surfaces of the glass slips. They were intended to 

 afford the means for collecting and cariying to earth any 

 part of the charges from the inductors, but the earth con- 

 nexion has not been necessary. 



When at work the charges passing from the disks to the 

 brushes may be heard some considerable distance; they 

 resemble the beating of the floats of a paddle-wheel. 



The charges are, however, reduced about 25 per cent, by 

 the addition of the sectors. 



