Wisconsin State Agricultural Society. 
97 
others taking their place, till the whole charge is carried off. 
DISTRIBUTION OF ELECTRICITY. 
It is an obvious inference from the theory, that free electric¬ 
ity must, from the mutual repulsion of its particles, exist only on 
or near the surface of bodies. Experiment shows this. If a hollow 
globe of metal, with an opening in the top, be insulated and elec¬ 
trified, a small pith ball, coated with gold leaf and suspended by a 
silk thread, when brought in contact with the inner surface 
receives no charge, but when made to touch the outer surface, is 
instantly electrified and repelled. In the same way it may be 
shown that if there be depressions or cavities in a charged con¬ 
ductor, there is no free electricity on the depressed surfaces. This 
fact is established by a great variety of experiments. 
In all bodies of regular form, the distribution of the fluid can, 
according to the theory, be mathematically calculated, and the 
results of such calculations have been confirmed by experiment. If 
the body be a sphere of metal, the fluid will be uniformly distrib¬ 
uted over the surface. If it be cylindrical and terminate in spherical 
surfaces, the fluid will accumulate more at the tw^o ends. If one 
end be drawn out more and more towards a point, the fluid will 
accumulate more and more at that end, till at length its tension will 
become too great to be retained. Accordingly it is found that an 
insulated conductor with a sharp point cannot be charged—or only 
very slightly—and that an electrified body is instantly discharged 
by holding a pointed conductor some distance from it. These 
facts are of importance in their bearing upon the construction of 
lightning-rods. 
INDUCTION. 
It is important to clearly understand the general fact of induction , 
which explains many electrical phenomena, and is intimately con¬ 
nected with the subject under consideration. In general we mean 
by induction , the electrical disturbance in one body produced by 
the proximity of another electrified body, when there is no transfer 
of electricity from one to the other. Clearly to apprenend this, let 
us again refer to our insulated globe. Suppose this to be highly 
charged w r ith positive electricity. Let now an insulated cylinder of 
7 A 
