104 On the Franklin'mn Theory 



lorlc, id always present in greater or smaller quantities in 

 the composition of bodies, and we have a right to conclude 

 that when its existence is not manifested bv its action it 

 nuist be in a comparative state, at It-ast, of rest and uni- 

 form dlfFuaion, since otherwise its passage would be indi- 

 cated by external signs or sensations. 



The facility with which the equilibrium is destroyed is 

 very striking : the fracture of scahng-wax, the fall of me- 

 tallic powders, the mere operation of pressure, are suffi- 

 cient for this purpose. JNlr. yEpinus pressed two plates of 

 glass close together : — when separated and insulated, each 

 acquired a strong electricitv, one positive, the other nega- 

 tive; and upon reunion, the electricitv of both disappeared: 

 it is obvious that these modes are inferior sorts of excita- 

 tion; but it is difficult, if not impossible, to offer anv so- 

 lution how excitation produces these eticcts : the means 

 seem to point: out a cause merely mechanical, but the pre- 

 sence of oxygen for some reason seems from experiment 

 to be requisite for their production. It is remarkable that 

 heat destroys the power of excitation, and dry cold aug- 

 ments it. 



The fourth proposition is a very important one, and upon 

 which a large proportion of electrical science depends — I 

 mean the distinction between conductors and electrics — in 

 Avhich it is assumed, that in conducting substances the elec- 

 tric fluid moves without obstruction ; and in electrics has 

 a very slow and dilticult, if any, passage. When we speak 

 hypothetically of conductors and electrics, we suppose them 

 to be perfect in their kind, but practically we are ignorant 

 of any such perfection. In metals which approach the 

 nearest to excellence, as conducting substances, there is 

 often a very obvious resistance to the passage of the fluid, 

 which is particularly remarkable in the destruction of small 

 wires by the charge of a battery, and the heating of their 

 substance even to redness and fusion ; tliouffh the most ac- 

 curate experiments have been hitherto insufficient to detect 

 any delay of motion by such resistance, or to perceive the 

 lapse of any tlic least time during its passage for several 

 miles. It has been nmch controverted uhether the fluid is 

 conveyed along the surface or through the substance of eun-. 

 dnctors ; but it does not appear to be a point of much con- 

 sequence, or which at all atlocts the consistency of the the- 

 ory. If a wire be coated with some electric substance, 

 such as wax, rts'n, &c. it will be found to conduct a charge 

 with as much fa(.ilii.y as before; and hence it is inferred 

 that the fluid must pass through the substance of tlic wirej 

 3 this 



