202 HISTOEY OF ELECTRICITY. 



of these to be a fluid which repelled its own parts and attracted those 

 of the other: this is, in fact, the outline of the theory which recently 

 has been considered as the best established ; but from various causes it 

 was not at once, or at least not generally adopted. The hypothesis 

 of the excess and defect of a single fluid is capable of being so treats i 

 as to give the same results with the hypothesis of two opposite fluids. 

 and happened to obtain the preference for some time. We have 

 already seen that this hypothesis, according to which electric pheno- 

 mena arose from the excess and defect of a generally diffused fluid, 

 suggested itself to Watson and Franklin about 1747. Watson found 

 that when an electric body was excited, the electricity was not created, 

 but collected ; and Franklin held, that when the Ley den jar was 

 charged, the quantity of electricity was unaltered, though its clistrilm 

 tion was changed. Symmer* maintained the existence of two fluids ; 

 and Cigna supplied the main defect which belonged to this tenet in 

 the way in which Dufay held it, by showing that the two opposite 

 electricities were usually produced at the same time. Still the appa- 

 rent simplicity of the hypothesis of one fluid procured it many support 

 ers. It was that which Franklin adopted, in his explanation of the 

 Leyden experiment; and though after the first conception of an 

 electrical charge as a disturbance of equilibrium, there was nothing in 

 the development or details of Franklin's views which deserved to win 

 for them any peculiar authority, his reputation, and his skill as a 

 writer, gave a considerable influence to his opinions. Indeed, for a 

 time he was considered, over a large part of Europe, as the creator of 

 the science, and the terms 3 Frank! inism, Franklinist, Frank-Union sys- 

 tem, occur in almost every page of continental publications on the sub- 

 ject. Yet the electrical phenomena to the knowledge of which 

 Franklin added least, those of induction, were those by which the pro- 

 gress of the theory was most promoted. These, as we have already 

 said, were at first explained by the hypothesis of electrical atmospheres. 

 Lord Mahon wrote a treatise, in which this hypothesis was mathema- 

 tically treated ; yet the hypothesis was very untenable, for it would 

 iot account for the most obvious cases of induction, such as the Leyden 

 jar, except the atmosphere was supposed to penetrate glass. 



The phenomena of electricity by induction, when fairly considered 

 by a person of clear notions of the relations of space and force, were 

 seen to accommodate themselves very generally to the conception 



2 Phil. Trans. 1759. Priestley, p. 160. 



