312 WRITINGS OF JOSEPH HENRY. [1855- 



No part of the writings of Franklin exhibits his sagacity 

 and his power of scientific generalization in a more conspic- 

 uous light than his theory of electricit}'. The talent to 

 discover isolated facts in any branch of science, although 

 possessed by few, is comparatively inferior to that character- 

 istic of mind which leads to the invention of an hypothesis 

 embracing in a few simple propositions whole classes of com- 

 plete phenomena. 



Theory of Electricity. 



According to the theory of Franklin all the facts of ordi- 

 nary electricity may be referred to the action of a subtle 

 fluid, which perhaps fills all inter-planetary space, and ma}'' 

 be the medium of light and heat. In order that the phe- 

 nomena of electricity may be represented by the mechanical 

 actions of this fluid, it is necessary to suppose that it is en- 

 dowed with certain properties and relations which may be 

 expressed in the following series of postulates : 



1st. The electric fluid (or sether) consists of atoms so min- 

 ute as to exist between the atoms of gross matter. 



2d. The atoms of the fluid repel each other with a force 

 varying inversely as the square of the distance; that is, 

 when the distances are 1, 2, 3, 4, 5, &c., the forces are 1, J, 



¥> rs"' "j^"' '^^^ 



3d. The atoms of the fluid attract the atoms of ordinary ' 

 matter with a force also varying inversely as the square of 

 the distance. 



4th. The atoms of gross matter devoid of electricity tend 

 to repel each other also with a force inversely as the square 

 of the distance. 



5th. The atoms of the fluid can move freely through cer- 

 tain bodies of gross matter, such as metals, water, &c., which 

 are hence called conductors, and cannot move, or but very 

 imperfectly, through other bodies, such as glass, baked wood, 

 dry air, &c., which are called non-conductors. 



6th. When each equal portion of space has the same amount 

 of electricity, and each body in it has so much of the same 

 fluid as to neutralize the attractions and repulsions of the 



