V.] JOSEPH PRIESTLEY. 107 



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. Nevertheless, his achieve- 

 ments are not only great in themselves, but truly 

 wonderful, if we consider the disadvantages under 

 which he laboured. 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 

 create apparatus out of washing tubs, he discovered 

 more new gases than all his predecessors put together 

 had done. He laid the foundations of gas analysis ; 

 he discovered the complementary actions of animal 

 and vegetable life upon the constituents of the atmo- 

 sphere; 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 com- 

 bustion, and is restored by green plants growing in 

 sunshine, was proved somewhat later. For these 

 brilliant discoveries, the Eoyal Society elected Priestley 

 a fellow and gave him their medal, while the Aca- 

 demies of Paris and St. Petersburg conferred their 



