38 
During the next decade Canton discovered the now commonly known 
difference between vitreous and resinous electricity. Beccaria experi- 
mented on the conducting power of water. Symmer made a number of 
experiments on the electrification of different kinds of fabrics by friction. 
and propounded a theory of two electric 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 experiments 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 are possessed by a number of other crystals. 
Aepinus made experiments in other branches of electricity, but he is 
chiefly noted for his ingenious single fluid theory of electricity. 
Between the years 1770 and 1780, the electric organs of the torpedo was 
one of the principal topics of discussion. The experiments of Walsh and 
Ingenhousz were the first to settle definitely the character of the peculiar 
power of the fish. 
The experiments of Cavendish belong to this period and were remark- 
able as being quantitative in their character. Considering the means at 
his command, the measurements made by this experimenter of the relative 
conducting powers of various substances must always excite admiration. 
Cavendish also proved the composition of water by causing different pro- 
portions of oxygen and hydrogen to unite by means of the electric spark. 
We now come to the classical experiments of Coulomb, who established 
the law of the variation of the electric force with distance to be that of the 
inverse square: a law which had previously been inferred from experi- 
ments on spheres by Dr. Robinson, who, however, did not publish his re- 
sults. Coulomb made an elaborate series of experiments ou the distribu- 
tion of electricity over charged conductors as influenced by shape and the 
proximity of other charged bodies. His theoretical and experimental work 
formed the basis of the mathematical theory as developed shortly after- 
wards by Laplace, Biot, and Poisson; the work of the latter being particu- 
larly important. 
Toward the end of the eighteenth century were made the important 
researches of Laplace, Lavoisier, and Volta, and of Sausure on the elee- 
tricity produced by evaporation and combustion. This is a subject des- 
tined to figure prominently again in the future; and in its rise there is in 
