JOSEPH PRIESTLEY. 97 



A dozen years later, one of the most sagacious and accurate in- 

 vestigators who has adorned this or any other country, Henry Cav- 

 endish, published a memoir in the " Philosophical Transactions," in 

 which he deals not only with the " fixed air " (now called carbonic 

 acid or carbonic anhydride) of Black, but with " inflammable air," or 

 what we now term hydrogen. 



By the rigorous application of weight and measure to all his pro- 

 cesses, Cavendish implied the belief subsequently formulated by La- 

 voisier, that, in chemical processes, matter is neither created nor de- 

 stroyed, and indicated the path along which all future explorers must 

 travel. Nor did he himself halt until this path led him, in 1784, to 

 the brilliant and fundamental discovery that water is composed of two 

 gases united in fixed and constant proportions. 



It is a trying ordeal for any man to be compared with Black and 

 Cavendish, and Priestley cannot be said to stand on their level. Nev- 

 ertheless, his achievements are not only great in themselves, but truly 

 wonderful, if we consider the disadvantages under which he labored. 

 Without the careful scientific training of Black, without the leisure 

 and appliances secured by the wealth of Cavendish, he scaled the 

 walls of science as so many Englishmen have done before and since 

 his day ; and, trusting to mother-wit to supply the place of training, 

 and to ingenuity to ci-eate apparatus out of washing-tubs, he discov- 

 ered more new gases than all his predecessors put together had done. 

 He laid the foundation of gas analysis ; he discovered the complemen- 

 tary actions of animal and vegetable life upon the constituents of the 

 atmosphere ; and, finally, he crowned his work, this day one hundred 

 years ago, by the discovery of that " pure dephlogisticated air " to 

 which the French chemists subsequently gave the name of oxygen. 

 Its importance, as the constituent of the atmosphere which disappears 

 in the processes of respiration and combustion, and is restored by 

 green plants growing in sunshine, w r as proved somewhat later. For 

 these brilliant discoveries the Royal Society elected Priestley a Fellow 

 and gave him their medal, while the Academies of Paris and St. Peters- 

 burg conferred their membership upon him. Edinburgh had made 

 him an honorary doctor of laws at an early period of his career ; but, 

 I need hardly add that a man of Priestley's opinions received no rec- 

 ognition from the universities of his own country. 



That Priestley's contributions to the knowledge of chemical fact 

 were of the greatest importance, and that they richly deserve all the 

 praise that has been awarded to them, is unquestionable ; but it must, 

 at the same time, be admitted that he had no comprehension of the 

 deeper significance of his work ; and, so far from contributing any 

 thing to the theory of the facts which he discovered, or assisting in 

 their rational explanation, his influence to the end of his life was 

 warmly exerted in favor of error. From first to last, he was a stiff 

 adherent of the phlogiston doctrine which was prevalent when his 

 VOL. vi. 1 



