ELECTRICAL EXCITATION BY RUBBING BODIES. 
31 
Any one of these became negative with the substances above, and positive with those 
beneath it. There are however many exceptions to this general statement : thus one 
part of a catskin is very negative to another part, and even to rock-crystal : different 
pieces of flannel also differ very much from each other. 
2142. The mode of rubbing also makes in some cases a great difference, although 
it is not easy to say why, since the particles that actually rub ought to present the 
same constant difference; a feather struck lightly against dry canvas will become 
strongly negative, and yet the same feather drawn with a little pressure between the 
folds of the same canvas will be strongly positive, and these effects alternate, so that 
it is easy to take away the one state in a moment by the degree of friction which 
produces the other state. When a piece of flannel is halved and the two pieces 
drawn across each other, the two pieces will have different states irregularly, or the 
same piece will have both states in different parts, or sometimes both pieces will be 
negative, in which case, doubtless, air must have been rendered positive, and then 
dissipated. 
2143. Ivory is remarkable in its condition. It is very difficult of excitement by 
friction with the metals, much more so than linen, cotton, wood, &c., which are 
lower in the scale than it (2141.), and withal are much better conductors, yet both 
circumstances would have led to the expectation that it would excite better than 
them when rubbed with metals. This property is probably very influential in giving 
character to it as a non-exciting steam passage (2102.). 
2144. Before concluding this paper, I will mention, that having used a thin ivory 
tube fixed in a cork (2076.) for many experiments with oil, resin, &c., it at last took 
up such a state as to give not merely a non-exciting passage for the steam, but to 
exert upon it a nullifying effect, for the jet of steam and water passing through it 
produced no excitation against any of the bodies opposed, as on the former occasion, 
to it (2099.). The tube was apparently quite clean, and was afterwards soaked in 
alcohol to remove any resin, but it retained this peculiar state. 
2145. Finally, I may say that the cause of the evolution of electricity by the libera- 
tion of confined steam is not evaporation ; and further, being, I believe, friction, 
it has no effect in producing, and is not connected with, the general electricity of the 
atmosphere : also, that as far as I have been able to proceed, pure gases, i. e. gases not 
mingled with solid or liquid particles, do not excite electricity by friction against 
solid or liquid substances*. 
References to papers in the Philosophical Magazine, 1840-1843. Armstrong, Phil. Mag. vol. xvii. pp. 
o70, 452 ; vol. xviii. pp. 50, 133, 328 ; vol. xix. p. 25 ; vol. xx. p. 5 ; vol. xxii. p. 1. Pattinson, Phil. Mag. 
vol. xvii. pp. 375 ; 457. Schafhaeutl, Phil. Mag. vol. xvii. p. 449 ; vol. xviii. pp. 14, 95, 265. 
