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posed to be, and, by using pure water, lie caused tbe electric spark 

 to become visible in it, a phenomenon capable of occurring only 

 through media almost nonconducting. In these experiments he 

 used thick glass tubes with wires led through the opposite ends, the 

 latter being sealed, and the tubes filled with water. These were 

 invariably shattered by the passage of the spark on account of the 

 accompanying elevation of temperature, which caused expansion. 

 He also established the facts that the atmosphere adjacent to an 

 electrified body acquires electrification of the same sign by abstract- 

 ing electricity from the body, and that the air then parts with its 

 electricity very slowly. He advanced the theory that there is a 

 mutual repulsion between the particles of the electric fluid and 

 those of air, and that a temporary vacuum is formed at the moment 

 of the passage of a disruptive discharge or spark. 



Robert Symmer, in 1759, described some most entertaining ex- 

 periments, making use of the opposite electrifications of superposed 

 stockings of different materials or merely of different colors (the dye 

 matters in the latter case causing differentiation). If, in a dry atmos- 

 phere, a silk stocking be drawn over the leg and a woolen one pulled 

 over it, the two w^ill be found, upon being removed, to be very power- 

 fully electrified in opposite senses. If the four stockings of two 

 such pairs be used and then suspended together, they will indulge 

 in remarkable antics due to each of the silk stockings trying to attract 

 both of the woolen ones, and vice versa, and, on the other hand, each 

 of each kind repelling the other. The amount of electrical attraction 

 and repulsion produced in this simple way in a dry atmosphere is 

 remarkable. The experiment may also be performed with all silk 

 stockings, one pair white and the other black. 



Symmer advanced the theory of two fluids coexisting in all matter 

 (not independently of each other, as had been previously supposed), 

 which by mutual counteractions produced all electrical phenomena. 

 His conception was that a body, positively electrified, did not exist 

 in that condition because of the possession of a charge of a positive 

 (as distinct from a negative) electric fluid which it had not held be- 

 fore, and did not hold in a normal state; nor that it possessed a 

 greater share of a single electric fluid than it did in an unelectrified 

 condition, as had been believed by Franklin and Watson, and by 

 Dufay respectively; but that such a body contained both positive 

 and negative electricities which, when the body behaved as " un- 

 electrified," entirely counteracted each other, but which, on th.e 

 other hand, caused a positive or negative charge to be evinced should 

 either positive or negative electricity respectively preponderate. 



a^^pinus was the author of another notable theory, of which we 

 must omit further mention for want of space. 



