Note 8 — GALVANISM, (continued 3)

In the description of a new air-pump of his invention, where he shows that electricity cannot pass through a vacuum, he adds: “There can be little doubt, from the above experiment, of the non-conducting power of a perfect vacuum; and this fact is still more strongly confirmed by the phænomena, which appear upon the admission of a very minute particle of air into the inside of the gauge. In this case, the whole becomes immediately luminous upon the slightest application of electricity; and a charge takes place, which continues to grow more and more powerful, in proportion as fresh air is admitted, till the density of the conducting medium arrives at its maximum. An Essay on Electricity, explaining the Theory and Practice of that useful Science. Third edit. London, 1787.