Astronomical and Nautical Collections. 329 
bodies to be distributed in any manner whatever within or without 
the hollow sphere; the sphere will be electrified by induction and 
the effect will be such that:— 
1. When all the electrified bodies are without the hollow sphere, 
their action, joined to that of the sphere, will give a result rquat 
tro zexo for all the space WITHIN THE CONCAVITY, as well as for 
the solid part of the sphere. 
2. When, on the contrary, all the electrical bodies are placed in, 
the interior concavity, the result of their action joined to that of the 
sphere, on a point without, will be a consTanT Force all around 
the body ar EQUAL DISTANCEs from its centre, and the same as if 
the whole of the two electric fluids were united in this point. The 
thickness of the electric stratum will be the same in all the extent 
of the exterior spherical surface, notwithstanding the different dis- 
tances of its different parts from the electrified bodies within ; and 
if the electricity passes by aspark from one of these bodies to ano- 
ther, or into the spherical shell, the exterior attractions and repul- 
sions will not be changed. 
Wir REGARD TO MAGNETISM, IT FoLLOWS FROM THIS THEO- 
REM THAT A MAGNETIC NEEDLE PLACED IN THE INTERIOR 
OF A HOLLOW SPHERE OF SOFT IRON, anv so smaLu 
AS NOT TO EXERT ANY SENSIBLE INFLUENCE ON THE SPHERE, 
WILL NOT BE SUBJECT TO ANY MAGNETIC ACTION, AND. WILL 
consEquentTLy NOT EXHIBIT ANY POLARITY. rvrom tur 
EFFECT OF THE EARTH’S MAGNETISM, OR FROM THAT OF ANY 
OTHER MAGNETS PLACED WITHOUT THE HOLLOW SPHERE. It 
follows also that if magnets are placed within such a sphere, their 
action on a small needle without it, joined to that of the shell itself 
as magnetized by their influence, will always produce a result 
equal to zero; for, from the second part of the theorem, the ex- 
terior action must be the same as if the boreal and austral fluids 
were both united in the centre of the sphere; which would neu- 
tralise their action at all distances, since these fluids are always 
necessarily present in equal quantities. And if we consider a plane 
as a sphere of infinite radius, we may infer that the interposition of 
a plate of soft iron of any given thickness, but of a great extent, 
