DISCOVERY BT MEANS OF NEW EXPERIMENTS. 535 



distribution of electricity on any part of a body, might be 

 measured, and found that the distribution agreed with the 

 theory of the self-repulsive power of each electricity. It 

 was by means of actual experiment that Canton, in the 

 year 1760, discovered the thermo-electric properties of 

 heated topaz; and Sulzer, in 1762, found the earliest 

 fact in voltaic electricity and electro-chemical action, viz., 

 that a piece of lead and a piece of silver, laid in mutual 

 contact upon the tongue so that both simultaneously 

 touched that organ, excited a peculiar sensation and taste. 

 Haiiy, by experiments made in the years 1785 to 1787, 

 discovered the thermo-electric properties of mesotype and 

 prehnite, and rediscovered those of sphene and calamine, 

 and also discovered several general truths in thermo- 

 electricity ; and he further found that Iceland spar, and 

 various other crystals, became electric by pressure. In 

 1786 Bennet discovered that electricity was produced by 

 the sifting of powders ; and, during the following year, 

 that the fracture of bodies produced electricity. About 

 the year 1787 M. Brard found that some crystals of axinite 

 became electric when heated. In the year 1791, Haiiy 

 found, by actual trial, that boracite was thermo-electric. 

 Keir, in the same year, discovered by experiment that 

 iron and some other metals could be rendered passive and 

 insoluble in acids. 



By means of experiments, made in the year 1795, 

 Dr. Wells discovered that charcoal conducted voltaic elec- 

 tricity, and might be used to produce it. It was by expe- 

 rimenting upon the effects of a voltaic current that 

 Nicholson and Carlisle, in the year 1800, discovered that 

 when the two ends of the wires which conveyed the current 

 were immersed in water, bubbles of gas arose from them. 

 By examining those gases, they found that one was oxygen 

 and the other hydrogen ; also, by applying litmus-paper, 



