Mr. W. R. Pidgeon on an Influence- Machine. 565 



contact-knob which peeps above it. Each of the earthing- 

 brushes, E, passes through and supports a fixed insulated in- 

 ductor, I, which is formed of tinfoil stuck to an ebonite backing 

 and insulated with wax. The surface of the wax on all the 

 inductors and disks is carefully varnished several times with 

 filtered shellac to protect the wax and give it a hard surface. 

 Each inductor is kept charged by a stationary point, P, con- 

 nected to it and placed so as to collect, from the revolving disk, 

 shortly before the main collecting brushes C. The sectors on 

 each of the disks are earthed at the moment when they are 

 passing between the opposite disk on the one hand and the 

 fixed inductor on the other, both of which carry a charge of 

 the same sign. The sectors therefore receive their charge at 

 a moment when their capacity is at a maximum, owing to 

 their standing between two charged inductors. As each 

 sector moves away from the brush to the right and out of the 

 influence of the inductor its capacity decreases, and therefore 

 its potential rises, and when it is opposite the point at which 

 its fellow disk is being earthed, its potential is proportionately 

 much higher than in the Wimshurst form of machine : and it 

 therefore induces a proportionately higher charge on the 

 sector being earthed. This sector, as it moves away from its 

 inductor to the left, again rises in potential ; and on arriving 

 at the earthing-brush induces a still higher potential on the 

 sectors moving to the right. This cumulative action goes on 

 in a sort of geometrical progression until, as a matter of fact, 

 the output of this form of machine rises to about four times 

 that of a Wimshurst of a similar size when measured by the 

 overflow of a leyden-jar (25 oz.). 



It may help to make the action of the machine more clear 

 if we regard it from the point of view of its being a condenser, 

 the plates of which can be charged in one position, then 

 shuffled, to bring the positives and negatives together, and 

 thus discharged. For the fact that each sector is imbedded 

 in an insulator enables it to receive a charge on each face as 

 it stands between the disk and the inductor, like a plate in a 

 condenser. It therefore carries forward a double charge, so 

 to speak, as compared with that carried forward by a machine 

 without inductors. Again, the drop of capacity and con- 

 sequent rise in potential of the sector as it moves away from 

 the inductor is so great, that the induction of the machine is 

 also practically doubled, and hence the total output is mul- 

 tiplied by four. That is to say, a machine having inductors 

 which act upon numerous insulated sectors is equivalent in 

 output to four machines of the same size of the ordinary 

 type. 



