ELECTRICITY. 



135 



TROPHORUS, and subsequently to the common CONDENSEK, which, combined 

 with the electroscope, became in electricity an instrument of investigation 

 analogous in its character and importance to the compound microscope in optics. 



The manner in which the electrified fluid is distributed upon insulated elec- 

 trified conductors next became the subject of inquiry. Beccaria showed that 

 its distribution is superficial, and that the internal parts of the electrified body 

 are in their natural state. It was shown that, whether the electrified conduc- 

 tor were hollow or solid, the electricity contained on it was the same. Le- 

 monnier first showed that the form of the conductor had an influence on the quan- 

 tity and the distribution of the fluids. 



In 1778 Volta published a memoir on this subject, in which he proved, that 

 of two cylinders of equal superficial dimensions, that which had the greater 

 length would receive, cater is paribus, the stronger charge, and inferred that 

 great advantage would arise from the substitution of a system of small cylin- 

 ders for the large conductors of electrical machines. About the same period, 

 he showed how inflammable gases could be ignited in close glass receivers by 

 the electric spark, the apparatus for which purpose soon grew into his eudiom- 

 eter, for the analysis of gases. Soon after this, the same apparatus supplied 

 the means of inflaming a mixture of oxygen and hydrogen gas, which led to 

 the discovery of the composition of water. 



In the year 1759 appeared, in the " Philosophical Transactions," a series of 

 papers by Mr. Robert Symmer, which are entitled to be recorded in the histo- 

 ry of electricity ; not so much on account of what they describe, as for the 

 theoretical views developed in them. The experiments of Symmer consisted 

 chiefly in exhibiting, by striking examples, the effect of the mutual attraction 

 of bodies electrified by opposite kinds of electricity. These results led him 

 to doubt the sufficiency of the Franklinian theory, then and long afterward uni- 

 versally received, to explain satisfactorily the phenomena ; and he was led to 

 consider whether the hypothesis of Dufaye might not be so modified as to ex- 

 plain them more adequately. Dufaye, as has been already stated, assumed the 

 existence of two independent electric fluids, which he supposed to be latent 

 in two distinct classes of bodies, the one in bodies of a vitreous, and the other 

 in bodies of a resinous nature ; and that these fluids, while they were each 

 self-repulsive, were mutually attractive of each other. 



It was obvious that such an hypothesis was quite inconsistent with the known 

 phenomena of electricity, even limited as they were in variety at the period 

 now referred to. Symmer retained the supposition of Dufaye so far as regard- 

 ed the assumed existence of two distinct fluids mutually attractive, but he main- 

 tained that these fluids were not independent of each other. On the contrary, 

 he assumed that they were always co-existent in bodies not electrified ; that, 

 by their natural attraction, they held each other in subjection ; that every body 

 in its natural state contained equal quantities of these fluids, each molecule of 

 the vitreous fluid being combined with a molecule of the resinous fluid, the 

 compound molecule thus formed exciting neither attraction nor repulsion on the 

 other parts of the natural fluid. 



This theory of two fluids was left by its author unsupported by any exten- 

 sive application to the phenomena which could be expected to shake the con- 

 fidence then generally given to the hypothesis of Franklin ; and although it is 

 noticed at some length in his history of electricity by Dr. Priestley, it obtained 

 no countenance or support until further advances in electrical experiments ren- 

 dered apparent the defects of the theory of a single fluid. It may be here ob- 

 served, that the French writers generally ascribe the theory of two fluids to 

 Dufaye, and are silent as to Symmer's share in it ; with what justice will be 

 apparent from what has been above stated. 



