86 Sir W. Snow Harris’s Researches in Statical Electricity. 
placed in an outer glass vessel A D, also filled with mercury; we 
have then all the conditions requisite for imparting a charge to 
the interior of the glass. For this purpose let a light insulated 
charging rod, ¢ 4, surmounted by an electrometer of repulsion, m, 
be introduced within the globe, and the mercury in the exterior 
vessel be connected with the ground by a metallic communica- 
tion, a¢. Let this system be charged in the usual way: when 
charged to any degree of intensity, as shown by the electrometer, 
remove the communication with the earth a ¢, and also the 
charging rod ¢b, by means of its insulating support &; run off 
the mercury first from the outer vessel AD, and then from the 
interior of the globe by means of a glass siphon, and place the 
now empty globe on an insulator, as represented, fig. 6. We 
may be now assured, on the faith of Franklin’s celebrated expe- 
rimeut of the electrical jar with moveable coatings, that all the 
interior surface of the globe is covered with electricity. Intro- 
duce now a small insulated carrier-ball 5 into this charged globe 
so as to touch the interior electrified glass, and again withdraw 
it. The carrier-ball comes away quite neutral, as in the case of — 
the hollow metal globe, notwithstanding that it has been actually 
brought into contact with a dense stratum of electricity, the pre- 
sence of which may be made evident by simply attaching the 
carrier-ball to the lower point 4 of the insulated charging rod be, 
fig. 5, and introducing it as before. The electrometer m will, 
if delicately hung, be immediately affected; or otherwise the 
charge may be shown by the medium of an ordinary gold 
leaf. . 
8. That the failure of the carrier-ball to take up electricity is 
in no degree dependent on the circumstance of what may be con- 
sidered in the light of electrical accumulation on an insulating 
surface as distinguishable from the case of the hollow metal 
sphere, may be clearly shown by charging a plane glass surface 
having moveable coatings and treating the plane charged glass 
in a similar way. In this case electricity is freely taken up by 
the carrier-ball from the charged side: it is hence evident that 
the globular form of the surface is the immediate cause of the 
failure of the carrier-ball to take up electricity from the glass. 
The carrier-ball, in fact, cannot take on that induced electrical 
state (3) requisite to its reception of free electricity ; the forces 
operating on it being in contrary directions, its natural electricity 
cannot recede from any point of its surface, hence all induced 
change in the distribution of its own proper electricity, np, fig. 2, 
is impossible. 
This experiment with charged glass may be effectively ma- 
naged by employing water instead of mercury ; or we may en- 
velope the outer surface of the globe in tinfoil and electrify the 
