58 ELEMENTS OF STATIC ELECTRICITY. 



sphere without altering the electrical conditions named, 

 it is evident that, A charge of electricity communicated 

 to any solid conductor will be condensed on its surface. 



SURFACE TRANSMISSION. It is also evident, that 

 although a static charge will be thus condensed on the 

 surface, electric transmission is not confined to the sur- 

 face ; since surface condensation is due to induction 

 and repulsion, which implies the possibility of trans- 

 mission through the substance to reach the surface. 



Hence, although induction operates during transmis- 

 sion, it cannot prevent transmission through the sub- 

 stance : so that it must not be inferred that the con- 

 ducting power is in proportion to the surface, but to the 

 mass of the conductor. 



Hence a charge of electricity which could be easily 

 transmitted by a solid rod might be sufficient to melt 

 a thin tube of the same diameter. 



HOLLOW CONDUCTORS. The same reasoning which 

 applies to an electric charge on a solid sphere will also 

 apply to one on a hollow sphere. For if any number of 

 the spherical shells composing the interior be removed, 

 it does not alter the equipotential of the remaining 

 ones, nor of their radii ; neither can it change the induc- 

 tion of the outside surroundings. 



And as the form may be altered without changing 

 these electric conditions, the same reasoning will apply 

 to any hollow conductor. 



Hence, A static electric charge, communicated to a hol- 

 low conductor, will be condensed on its external surface. 



PROOF PLANE But all our conclusions should be 

 the result of experiment ; to aid us in which we now 

 require the little instrument called the proof plane, 

 represented in Fig. 8 ; which consists of a small brass 



