Maech 18, 1898.] 



SCIENCE. 



363 



Bpired by the receipt of a Leyden jar from 

 a friend, Wm. Collinson, of London. He 

 propounded the theorj^ of positive and neg- 

 ative fluids, which has lately, in a modified 

 form, been brought so prominently into no- 

 tice again by the writings of Lodge, and he 

 made an investigation of the principle of 

 the Leyden jar, but the most important of 

 his researches relate to the identification of 

 electricity and lightning. The probable 

 identity of the two phenomena had been 

 hinted at, as we have seen, by several ob- 

 servers, but Franklin went systematically to 

 work to test the hypothesis. Under date of 

 November 7, 1749, the following passage is 

 found in his note-book : " Electric fluid 

 agrees with lightning in these particulars : 

 (1) Giving light. (2) Color of the light. 

 (3) Crooked direction. (4) Swift motion. 

 (5) Being conducted by metals. (6) Crack 

 or noise in exploding. (7) Subsisting in 

 water or ice. (8) Rending bodies in pass- 

 ing through. (9) Destroying animals. (10) 

 Melting metals. (11) Firing inflammable 

 substances. (12) Sulphureous smell. The 

 electric fiuid is attracted by points ; we do 

 not know whether this property is in light- 

 ning. But since they agree in all the partic- 

 ulars wherein we can already compare them, 

 is it not probable that they agree likewise in 

 this? Let the experiment be made." The 

 hypothesis was elaborated and sent to his 

 friend Collinson, who communicated it to the 

 Boyal Society. This Society rather ridi- 

 culed Franklin's ideas at first, but his paper 

 was published in London and also in 

 France, and attracted considerable atten- 

 tion. 



The experiment was first made in France 

 by M. d' Alibard, at Marli, on May 10, 

 1752, and it was repeated shortly after- 

 wards by M. de Lor, in Paris. The results 

 of what were called the Philadelphia ex- 

 periments were communicated to the Royal 

 Society and caused quite a stir in scientific 

 circles. It is right to say, with regard to 



the Royal Society, that Franklin's claims 

 to scientific recognition were championed 

 by Sir William "Watson, and were fully en- 

 dorsed by the Society by his election to a 

 Fellowship and the award of the Copley 

 Medal, together with the free donation of 

 the Society's Transactions during his life. 



Franklin's own experiments with kites 

 are well known, as is also the method of 

 protecting buildings from lightning which 

 was introduced by. him and is still very 

 widely used, although it has been greatly 

 abused by the lightning-rod man. 



During the next decade Canton discov- 

 ered the now commonly known difference 

 between vitreous and resinous electricity. 

 Beccaria experimented on the conducting 

 power of water. Symmer made a number 

 of interesting experiments on the electrifi- 

 cation of different kinds of fabrics by fric- 

 tion, and propounded a theory of two elec- 

 tric fluids. Contemporaneous with these 

 were a number of other experimenters who 

 added to the stock of knowledge of this 

 class of phenomena. 



The experiments of Aepinus and others 

 on the pyroelectric properties of tourmaline 

 now began to attract attention. The ex- 

 periments of the Abbe Haiiy are perhaps 

 the most important in this connection at 

 this stage of the subject. He found the 

 polar properties of the crystal and showed 

 that similar properties were possessed by 

 a number of other crystals. Aepinus made 

 experiments in other branches of electricity, 

 but he is chiefly noted for his ingenious sin- 

 gle-fluid theory of electricity. 



Between the years 1770 and 1780 the 

 electrical organs of the torpedo were one of 

 the principal topics of discussion. The ex- 

 periments of Walsh and Ingenhousz were 

 the first to definitely settle the character of 

 the peculiar power of the fish. 



The experiments of Cavendish belong to 

 this period and were remarkable as being 

 quantitative in their character. Consider- 



