40 HISTORY OF ELECTRICITY. 



electricity and the mutual gravitation of matter, 

 are accounted for by the same hypothesis of a 

 single fluid or ether. A theory which offers a pro- 

 spect of such a generalization is worth attention ; 

 but a very clear and comprehensive view of the 

 doctrines of several sciences is requisite to prepare 

 us to estimate its value and probable success. 



Question of the Material Reality of the Electric 

 Fluid. At first sight, the beautiful accordance of 

 the experiments with calculations founded upon the 

 attractions and repulsions of the two hypothetical 

 fluids, persuade us that the hypothesis must be the 

 real state of things. But we have already learned 

 that we must not trust such evidence too readily. 

 It is a curious instance of the mutual influence of 

 the histories of two provinces of science, but I 

 think it will be allowed to be just, to say that the 

 discovery of the polarization of heat has done much 

 to shake the theory of the electric fluids as a phy- 

 sical reality. For the doctrine of a material caloric 

 appeared to be proved (from the laws of conduction 

 and radiation) by the same kind of mathematical 

 evidence (the agreement of the laws respecting the 

 elementary actions with those of fluids.) which we 

 have for the doctrine of material electricity. Yet 

 we now seem to see that heat cannot be matter, 

 since its rays have sides, in a manner in which a 

 stream of particles of matter cannot have sides, 

 without inadmissible hypotheses. We see, then, 

 that it will not be contrary to precedent, if our 



