THE GROWTH OF SCIENCE IN THE NINETEENTH CENTURY. 167 



and the clear exposition of the full meaning of Priestley's discover}^, 

 while the knowledge of the composition of water, the necessary com- 

 plement of the knowledge of oxygen, came to us through Cavendish 

 and, we may perhaps add, through Watt. 



The date of Priestley's discovery of oxygen is 1774, Lavoisier's 

 classic memoir ''On the nature of the principle which enters into com- 

 bination with metals during calcination" appeared in 1775, and (caven- 

 dish's paper on the composition of water did not see the light until 1784. 



During the last quarter of the eighteenth century this new idea of 

 oxygen and oxidation was struggling into existence. How new was 

 the idea is illustrated by the fact that Lavoisier himself at tirst spoke 

 of that which he was afterwards, namely, in 1778, led to call oxygen, 

 the name by which it has since been known, as "the principle which 

 enters into combination." What difficulties its acceptance met with is 

 illustrated by the fact that Priestley himself refused to the end of his 

 life to grasp the true bearings of the discovery which he had made. 

 In the 3"ear 1799 the knowledge of oxygen, of the nature of water and 

 of air, and indeed the true conception of chemical composition and 

 chemical change, was hardly more than beginning to be, and the cen- 

 tury had to pass wholl}^ awa}' before the next great chemical idea, 

 which we know by the name of the atomic theory of John Dal ton, was 

 made knowMi. We have only to read the scientific literature of the 

 time to recognize that a truth which is now not onl}- woven as a master 

 thread into all our scientific conceptions, but even enters largely 

 into the everj'day talk and thoughts of educated people, was a hundred 

 years ago struggling into existence among the philosophers themselves. 

 It was all but absolutely unknown to the large world outside those 

 select few. 



If there be one word of science which is writ large on the life of 

 the present time, it is the word "electricity.'" It is, I take it, writ 

 larger than any other word. The knowledge which it denotes has 

 carried its practical results far and wide into our dail}' life, while the 

 theoretical conceptions which it signifies pierce deep into the nature 

 of things. We are to-day proud, and justly proud, both of the mate- 

 rial triumphs and of the intellectual gains which it has brought us, and 

 we are full of even largei" hopes of it in the future. 



At what time did this bright child of the nineteenth centur}^ have 

 its birth J' 



He who listened to the small group of philosophers of Dover, who 

 in 1799 might have discoursed of natural knowledge, w^ould perhaps 

 have heard nuich of electric machines, of electric sparks, of the electric 

 fluid, and even of positive and negative electricit}' ; for frictional elec- 

 tricity had long been known and even carefully studied. Probably 

 one or more of the group, dwelling on the observations which Galvani, an 

 Italian, had made know n some twenty years before, developed views on 



