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effect whatever, their machines working equally well without 

 it. For my own part, after having experimented with this 

 appendage in various forms, I have laid it aside, replacing it by 

 an ebonite ball. These ebonite balls, I may remarli, I have 

 found to be much more effective than brass for the prevention 

 of the escape of electricity. 



My next experiment was on the rubbers, the stuffing of 

 which is commonly of horse-hair, but in my machine is com- 

 posed of sheet-indiarubber about half -inch thick, covered with 

 sheepskin, which forms a good flat surface, and fits closely to 

 the plate. 



I thought by raising these rubbers higher there would be 

 less time for the charge to escape from the friction plate before 

 its coming opposite the di-electric, but after having raised 

 them one and a-half inches there was no perceptible difference. 



While speaking of the rubbers, I may remark that it is a 

 very common opinion that the electricity generated by the one 

 on the side of the plate farthest from the di-electric is lost or 

 wasted, but that such is not the case is easily proved, as one 

 can be laid off; and we find on applying them alternately that 

 the most distant one is qnite as effective as the other. 



My next experiment was on the spindle of the upper disc, 

 which being of iron allowed some of th^ electricity to escape. 

 This spindle I replaced by one made of ebonite, but the slight 

 advantage gained was so small that it was more than counter- 

 balanced by the loss in stiffness; so I laid this aside, and again 

 used the iron one. This spindle I have insulated from the disc. 



I next tried the effect of lengthening the upper comb by 

 means of an additional point projecting from the lower ball of 

 the same. This proved to be a decided disadvantage, as it con- 

 siderably diminished the length of spark, the reason being, as 

 I afterwards found, that the di-electric — while it is from the 

 circumference to a certain distance inwards negatively charged 

 — has at the same time its central parts and spindle equally 

 charged with positive electricity ; and so the extra point ap- 

 proaching too near this central portion, instead of receiving an 

 addition, gave up a part of what the comb had already 

 gathered. 



As there exists a diversity of opinion as to the best form of 

 collectors, many, being highly in favour of those used in 

 " Winter's" machine — which are made in the form of a ring, 

 and having the points set in a groove — I constructed a pair on 

 this plan. These I found not quite so effective as the forks, 

 but this, I think, is to be attributed to their diameter being 

 somewhat less than the length of the forks ; otherwise I think 

 their performance would have been very nearly equal. 



My next experiment consisted in the introduction of the 



