%68 Mr. W. R. Pidgeon on an Influence- Machine. 



becomes charged negatively. Passing on it induces a posi- 

 tive charge on the other disk at the next neutralizing brush 

 J)', and ultimately meets a similar negative charge, borne 

 forward by the other disk, at E, where it discharges into the 

 negative collector. I do not mean that this is a full explana- 

 tion of all that takes place, but I hope by its means to show 

 the lines along which I worked in designing the machine 

 before you. I thought that what had to be done was : — 1st, to 

 make the capacity of each sector on the disk as great as 

 possible while being charged at D, and as small as possible 

 while being discharged at E, so that the amount of electricity 

 displaced by each sector should be as large as possible. 2nd. 

 To prevent any leak-back of electricity from sector to sector 

 as they are entering, or leaving, the different fields of induc- 

 tion. 3rd. To make the sectors large and numerous so as to 

 increase the capacity of the machine. And it was with these 

 objects in view that I built the machine which I will now 

 describe. The disks are made of ebonite | inch thick and 

 are recessed as shown in the drawing, § inch deep x 5| 

 inches wide. There are 32 sectors on each disk made of thin 

 sheet-brass, and having short brass wires soldered to them on 

 to which the small brass collecting-knobs are screwed. The 

 sectors were arranged in the recess as shown on the drawing, 

 the wires attached to them were passed through holes in the 

 disk, and the knobs screwed on from the back. The recess 

 was then filled up to slightly above the level of the face of the 

 disk with melted wax composed of equal parts by weight of 

 paraffin and rosin, and when cold the excess wax was turned off 

 in the lathe. Each sector is thus entirely imbedded in an 

 insulating material, the only exposed part, from w T hich the 

 charge might brush back from sector to sector, being the 

 small brass knob. In order to minimize this possible leak the 

 sectors are set at an angle to any radius, as shown on the 

 drawing, so that a sector on one disk does not pass a sector on 

 the opposite one suddenly, but does so with a sort of shearing- 

 motion requiring four times the angular movement of the disks 

 for the sectors to clear one another than would be needed 

 were they placed radially. By the time, moreover, that any 

 one sector has entirely entered a field of induction, the next 

 following sector is three parts into the field, and the next 

 behind that again is half in, while the third is one fourth the 

 way in, and the fourth just entering, so that the maximum 

 difference of potential between any two neighbouring knobs 

 is reduced to one fourth of what it would be were the sectors 

 arranged radially. This angular arrangement of the sectors 

 naturally necessitates the collecting and neutralizing brushes 



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