592 SPECIAL METHODS OF DISCOVERY. 



which accounts for a great part of the irregularities, and, 

 if I may use the termf the caprices that seem to accom- 

 pany most of the experiments in electricity. This prin- 

 ciple is, that electric bodies attract all those that are not 

 so, and repel them as soon as they become electric by the 

 vicinity or contact of the electric body. . . . Upon apply- 

 ing this principle to various experiments in electricity, 

 anyone will be surprised at the number of obscure and 

 puzzling facts which it clears up.' * Chance has thrown in 

 my way another principle more universal and remarkable 

 than the preceding one, and which casts a new light upon 

 the subject of electricity. The principle is, that there are 

 two distinct kinds of electricity very different from one 

 another, one of which I call vitreous, the other resinous 

 electricity. The first is that of glass, gems, hair, wool, 

 &c. ; the second is that of amber, gum-lac, silk, &c. The 

 characteristic of these two electricities is that they repel 

 themselves and attract each other.' In 1759, Symmer 

 also inferred from known facts the hypothesis of two oppo- 

 site kinds of electricity. In 1708, Dr. Wall inferred that 

 because electricity produces sound and light, it ' seems 

 in some degree to represent thunder and lightning.' By 

 studying the additional truths respecting electricity and 

 lightning which had been subsequently acquired, and 

 observing that the effects of those forces were usually 

 alike, Dr. Franklin, in 1749, concluded that they were 

 identical, and was thus led to devise his electric kite, by 

 experimenting with which he proved his hypothesis and 

 made the discovery. 



In 1760, Mayer inferred, and Coulomb confirmed, the 

 theory that magnetic attraction varies inversely as the 

 square of the distance, except at short distances. In 1799, 

 Fabroni inferred that voltaic electricity might be an effect 

 of chemical action ; in 1831, Wollaston also concluded that 



