CONTRIBUTIONS TO SCIENCE. 559 



conductor on account of the increased area of the surface, 

 but the displacement continuing until some external con- 

 ductor is reached through which the circuit is completed. 

 Thus, when we say that the charge of a body is increased, 

 we mean that positive electricity is communicated to it 

 through an electrode, but we know that an equal amount 

 passes out of the body through its external surface and is 

 squeezed into the dielectric, and it is this dielectric which is 

 the only portion of the system really affected by the charge, 

 and in which the whole energy of the charged body resides. 

 This view has very recently been put forth under the title 

 of The Conservation of Electricity. According to Maxwell's 

 view of the constitution of dielectrics, the squeezing of a 

 quantity of electricity into a dielectric does not imply a con- 

 densation of the electricity, but a strain in the dielectric on 

 account of the displacement of the electricity, which cannot 

 move without distorting the " cells " of which the dielectric 

 is supposed to be made up. 



7. Ever since men began to think about Nature, philoso- 

 phers have differed in their views respecting the primary 

 constitution of bodies. When, with all the freshness of a first 

 impulse, though unprovided with the barest means of verifi- 

 cation, the human mind first went forth in search of physical 

 truth, two paths at once appeared, leading to opposite poles, 

 and both were trodden by pilgrims full of hope. Some found 

 their satisfaction in contemplating the continuous fulness of 

 the universe. They could imagine no gap in Nature, whose 

 endless variety they were contented to refer to a principle 

 of infinite divisibility and to the inter-play of contiguous 

 elements whose changes were ordered by the mind that was 

 interfused with all. To others, of a more analytical turn, it 

 appeared impossible to account for the most obvious pheno- 

 mena, except by the hypothesis of atoms moving in a void. 



The penetrating intellect of Democritus had early given 

 consistency to an atomic theory, which became the founda- 

 tion of the system of Epicurus. Yet, widely as this 

 philosophy prevailed at certain periods, the doctrine of a 



