PRELIMINARY NOTIONS. 5 



under the form of mechanical work or of heat, the energy which 

 has been communicated to them in one or the other of these 

 forms by natural forces or agencies, such as waterfalls, muscular 

 power, air in motion, chemical actions, &c. The electricity 

 developed in the course of this transformation is only an inter- 

 mediary, and has no other function but to store energy, since 

 it always restores it under a mechanical, calorific, or chemical 

 form." 



HYPOTHESIS ON ELECTRIC PHENOMENA. In order to ex- 

 plain the electric phenomena, various theories have been put 

 forward which, although not possessing the characteristics of 

 absolute certainty, at all events enable one to realise the facts 

 and to form a sufficiently approximate idea of the actions which 

 are taking place. Amongst these theories, the two following 

 are the more generally adopted. 



Symmer admits the existence of two fluids, the one positive, 

 the other negative, and entering into the composition of every 

 substance. A body containing equal quantities of these two 

 fluids would be in a neutral state ; and a body containing un- 

 equal quantities of both fluids would be positively or negatively 

 electrified according to the nature of the fluid in excess. That 

 excess constitutes the free electricity of the body. The particles 

 of a similar fluid repel each other and attract those of the other 

 fluid. The power of attraction or of repulsion is in direct ratio 

 to the square of the distance. Symmer says that the propaga- 

 tion of electricity in a conductor is the result of decompositions 

 and recompositions of the neutral fluid. 



Franklin admitted the existence of one fluid only, the 

 molecules of which repel each other but attract ponderable 

 matter. This is equivalent to the conception of a non-ponderable 

 agent called electricity or electric fluid, existing in every body, 

 in quantities varying according to the nature of the said 

 bodies. If, as the result of a special action exerted upon any 

 other body, it becomes possessed of more electricity than in its 

 neutral state, the body is said to be positively electrified ; if, on 

 the contrary, the quantity of electricity which it contains 

 diminishes, it is said to be negatively electrified. In this theory 

 the phenomena of induction are explained by this consideration, 



