Mr. W. R. Pidgeon on an Influence- Machine. 267 



Further tests have been made by fixing a pulley, 3 in. in 

 diameter, to the overhanging end of the spindle, and sus- 

 pending therefrom by a cord a weight of 15 lbs. The fall of 

 this weight through three feet produced seventeen revolutions 

 when the disks were not excited and ten revolutions when 

 excited. The same Leyden jars were then connected, and it 

 was found that the foil of the weight through three feet pro- 

 duced twenty-eight sparks of oj in. length. Reducing this 

 to the terms of work in relation to sparking length, and 

 omitting friction of the machine, it will be seen that 1 lb. 

 weight falling through rather less than twelve inches produces 

 a spark of 3J in. length. It must not, however, be forgotten 

 that a considerable amount of electricity is also passing by 

 way of the neutralizing circuit. 



XXV. An Influence Machine. By W. R. PiDGEON*. 



IF we follow the action of any single sector on a disk of 

 one of Mr. Wimshurst's beautiful machines, we find it 

 goes through the following electrical changes : — Suppose it 

 to be just leaving the positive collector C, it comes into a 



Sectors 



Wax 



*m 



JZbonite 





u 



Section of Disk. 



strong positive field produced by the other disk, and while 



in this field is earthed by the first neutralizing brush D and 



* Communicated by the Physical Society : read June 23, 1893. 



T 2 



