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



W. E. Pidgeon's machine with one 







pair of plates — 







of 12 in. diam. requires 22 sq. ft. of 







area to pass the collecting-brushes 



A 15-in. Wimhurst same day requires 



per spark. 



64 sq. ft. 



per spark. 



of 17 in. diam. do. 17*1 sq. ft. do. 



A 15-in. do. 76 do. 



do. 



18 in. do. 18-5 do. 



A 15-in. do. 70 do. 



do. 



19 in. do. 19-4 do. 



A 15-in. do. 70 do. 



do. 



2 pairs of 27 in. do. 164 do. 







Average 17 - 85 sq. ft. 



Average... 70 sq. ft. 





Comparative efficiency nearly 4 to 1. 



Mr. Wimshurst's 8-plate 15-in. machine, which he kindly 

 tried for me himself, requires 97*07 sq. ft. per spark. 



The length of spark between knobs is approximately the 

 same as in a Wimshurst of the same size, but, if anything, 

 slightly less. If, however, the fixed inductors are taken away 

 and the wax disks run with the brushes on alone, the machine 

 gives much longer sparks; but its output is then decreased to 

 a little less than double that of a Wimshurst. 



My machine, 19 in., without inductors, requires 45 sq. ft. 

 per spark. 



The wax which covers the disks prevents the sectors leaking 

 from any point except the small brass contact-knobs, and 

 thus enables the machine to work in the dampest weather ; 

 in fact, it may be sponged with water, or have water squirted 

 at it, and yet will work if only it is first wiped up with a 

 duster. Dirt, likew ise, makes almost no difference ; and 

 usually the induction starts up before the disks have made a 

 revolution, even though the machine may have been left 

 standing for weeks. It will, moreover, work on short circuit; 

 and in all but the very worst weather, or after standing idle 

 for a long time, it is not necessary for any of the brushes to 

 actually touch the contact-knobs. 



The fact that the only place from which a sector can leak 

 electrically is from its small brass collecting-knob, makes it 

 possible to run disks so large as to almost touch the first 

 motion-shaft below or the collectors on either hand. This 

 obviously allows the machine to be snugged up, and so save 

 cupboard-room. 



The collectors have been covered with ebonite, and every- 

 thing has been done to expose as little naked surface as pos- 

 sible, partly for convenience in handling, but chiefly to enable 

 the machine to be used in bad weather. 



When exciting a Crookes or Jackson tube the knobs of the 

 dischargers should be brought to either end of the tube, the 

 terminals of wHch should also be capped with brass knobs 

 to prevent any brush-discharge. 



The tube should be of a sufficiently high resistance to use all 



