18G0.] on Atmospheric Electricity, 289 



and the speaker hoped soon to see the atmospheric electrometer 

 generally 'adopted as a useful and convenient weather-glass. 



The speaker could not conclude without guarding himself against 

 any imputation of having assumed the existence of two electric fluids 

 or substances, because he had frequently spoken of the vitreous and 

 resinous electricities. Dufay's very important discovery of two modes 

 or qualities of electrification, led his followers too readily to admit his 

 supposition of two distinct electric fluids. Franklin, iEpinus, and 

 Cavendish, with a hypothesis of one electric fluid, opened the way 

 for a juster appreciation of the unity of nature in electric phenomena. 

 Beccaria, with his " electric atmospheres," somewhat vaguely struggled 

 to see deeper into the working of electric force, but his views found 

 little" acceptance, and scarcely suggested inquiry or even meditation. 

 The 18th century made a school of science for itself in which, for the 

 not unnatural dogma of the earlier schoolmen "matter cannot act 

 where it is not," was substituted the most fantastic of paradoxes, 

 contact does ?iot exist. Boscovich's theory was the consummation of 

 the 18th century school of physical science. This strange idea took 

 deep root, and from it grew up a barren tree, exhausting the soil and 

 overshadowing the whole field of molecular investigation, on which so 

 much unavailing labour was spent by the great mathematicians of the 

 early part of our 19th century. If Boscovich's theory no longer 

 cumbers the ground, it is because one true philosopher required more 

 light for tracing lines of electric force. 



Mr. Faraday's investigation of electrostatic induction influences 

 now every department of physical speculation, and constitutes an era 

 in science. If we can no longer regard electric and magnetic fluids 

 attracting or repelling at a distance as realities, we may now also con- 

 template as a thing of the past that belief in atoms and in vacuum, 

 against which Leibnitz so earnestly contended in his memorable cor- 

 respondence with Dr. Samuel Clarke. 



We now look on space as full. We know that light is propagated, 

 like sound, through pressure and motion. We know that there is no 

 substance of caloric — that inscrutably minute motions cause the expan- 

 sion which the thermometer marks, and stimulate our sensation of heat 

 — that fire is not laid up in coal more than in this Leyden phial, or this 

 weight : there is potential fire in each. If electric force depends on a 

 residual surface action^ a resultant. of an inner tension experienced by 

 the insulating medium, we can conceive that electricity itself is to be 

 understood as not an accident, but an essence of matter. Whatever 

 electricity is, it seems quite certain that electricity in motion is heat ; 

 and that a certain alignment of axes of revolution in this motion is 

 magnetism. Faraday's magneto-optic experiment makes this not a 

 hypothesis, but a demonstrated conclusion. Thus a rifle bullet keeps 

 its point foremost ; Foucault's gyroscope finds the earth's axis of pal- 

 pable rotation ; and the magnetic needle shows that more subtle 

 rotatory movement in matter of the earth, which we call terrestrial 

 magnetism, all by one and the same dynamical action. 



