Biographical Memoir ofDr Priestley. 213 



tory of Electricity, that of Optics, and his Elements of Per- 

 spective *. 



The History of Electricity had the merit of making its ap- 

 pearance at an interesting period, when Franklin had just thrown 

 a most brilliant light upon this beautiful branch of natural phi- 

 losophy, and made the boldest application of it. It presented a 

 clear and accurate account of all th^t had been done in that de- 

 partment of science ; and being translated into several languages., 

 began to extend its author's reputation abroad. 



But abandoning the irksome labour of unfolding the disco- 

 veries of others, he lost no time to place himself among the ori- 

 ginal discoverers in physics. It is by his inquiries into the dif- 

 ferent kinds of gases, that he has especially merited this title, 

 and erected the most durable monument to his fame -f*. 



It had long been known, that several bodies allow air to 

 escape from them, and that others absorb it under certain cir- 

 cumstances. It had been remarked, that the air of sinks, at the 

 bottom of wells, and that which rises from liquids in a state of 

 fermentation, extinguishes light, and destroys organic beings. It 

 was also known, that a light gas exists in mines, rising most 

 commonly towards the roofs of subterranean vaults, and some- 

 times taking fire and producing great explosions. The former 

 received the name of Jioced air; the latter that of irtflammable 

 air. They are the same as those which we now call carbonic 

 a£id gas, and hydrogen gas. Cavendish determined their speci- 

 fic gravities : Black discovered that it is the fixed air which ren- 

 ders lime and the alkalies effervescent ; and Bergmann was not 

 long in detecting its acid quality. Such was the extent of know- 



* The History and present state of Electricity, London, 1767 and 1775, 

 4to : it has been translated into French by Brisson, Paris, 1771, 2 vols. 12mo. 

 ^The history and present state of the discoveries relative to Vision and Co- 

 lours, London, 1772, 2 vols. 4to — Familiar Introduction to the Theory and 

 Practice of Perspective, 1771, 8vo — He also published a Familiar Introduc- 

 tion to the Study of Electricity, 1768, 8vo. 



•\ Experiments and observations on the different kinds of Gases. The 

 first volume appeared in 1774, the third and last in 1779. This work was 

 continued, under the title of Experiments and Observations respecting va- 

 rious branches of Natural Philosophy, 3 vols. 8vo, the last published in 1786 

 at Birmingham. The whole were translated into French by Gibelin, in 6 vols. 

 12mo, Paris 1775 to 1780. 



