Sir W. Snow Harris’s Researches in Statical Electricity. 85 
of some magnitude, and a few light cylindrical rings, or a pro- 
jecting gilded reed nr, be added to the remote face m of the 
suspended disc », so as to allow the electricity of the near face of 
n to recede, and a determination of the charge toward the face p 
of the charged disc p to ensue, then considerable attractive force 
follows ; if, instead of suspending 7 by an insulating thread, we 
suspend it by a metallic thread, and connect p with a charged 
surface of great extension, then the attractive force is a maxi- 
mum. 
Exp. 3. Touch a charged surface with a small disc consisting 
of a thin lamina of varnished tale attached to a slender imsula- 
ting rod of glass; it takes up no charge, or at least so little that 
it often fails to affect a delicate electroscope. 
Exp. 4, Substitute an extremely thin conducting disc for the 
tale: similar results will ensue ; the quantity of electricity brought 
away will be often inappreciable, as the state of the atmosphere 
and other insulations become more or less perfect. Increase the 
thickness of the conducting disc: the quantity of electricity 
brought away will also increase, and up to a limit at which we 
give the touching face of the disc all the capacity for inductive 
change of which it is susceptible. 
These facts have an important application to the phenomena 
of statical electricity, and cannot be too forcibly insisted on: 
they may be easily and substantially verified experimentally. 
7. It is apparent from the experiments of Cavendish, Saussure, 
Volta, Coulomb, and other celebrated philosophers, that if a hol- 
low metal globe be insulated and charged (as it is termed) with 
electricity, all the charge will be found on its exterior surface ; 
so that a small carrier-ball perfectly imsulated on a slender 
support, takes up no charge after being introduced into the 
interior of the globe and placed in contact with its inner sur- 
face. There is no doubt that the charge is determined toward 
the exterior surface of the globe. A great variety of experi- 
mental evidence leads to this conclusion. Still the failure of an 
insulated carrier-ball to take up electricity from the interior sur- 
face of the globe is, taken abstractedly, by no means conclusive 
of the fact: it is quite possible for the whole interior of the globe 
to bristle, as it were, with electricity, and yet the carrier-ball fail 
to become charged in the slightest degree. This fact is of such 
great elementary importance, that I feel myself justified in call- 
ing attention to former experiments on this point, and which I 
have greatly extended and perfected. 
Exp. 5. Let ab, fig. 5, be a hollow globe of glass of about 5 
inches diameter, having a short neck at a, carefully varnished, 
and exposing an opening about an inch in diameter. Let 
this globe be filled with dry mercury up to the neck a, and be 
