THE AGE OF SCIENCE 239 



was not practical in the ordinary sense, and it was no 

 doubt often difficult for him to explain what he was doing. 

 His most important discovery was that of oxygen a dis- 

 covery that was made at the same time (1774) by the 

 English clergyman, Priestley. Chemists know that this is 

 one of the most important discoveries ever made in the 

 field of chemistry, and, filled with this conviction, in 1874, 

 one hundred years after the discovery was made, the chem- 

 ists of the United States made a pilgrimage to Northumber- 

 land on the Susquehanna to do honor to the memory of 

 Priestley, who there spent the last years of his life. 



But why was this discovery so important? Oxygen, to 

 be sure, is the most widely distributed and the most abund- 

 ant substance in and on the earth; it plays a controlling 

 part in the breathing of animals, and in most of the 

 changes that are taking place upon the earth ; a knowledge 

 of it and of the ways in which it acts has done more than 

 anything else to give chemists an insight into chemical 

 action in general ; and therefore has contributed more than 

 anything else to the development of chemistry. All this is 

 no doubt true, but are these results practical? Could we 

 go out into the world and form a company and sell stock 

 on the basis of such a discovery? Or could the discoverer 

 in any way realize in cash ? The average man of the world 

 would say: "No! there is nothing in it. It may be well 

 for a few men who have not the power to compete with 

 their fellow-men in the busy marts to devote themselves to 

 such useless pursuits. Possibly something may come of it 

 in time, but better something practical, something that 

 can be converted into hard cash. That is the test, and the 

 only fair test by which we can judge whether any partic- 

 ular piece of scientific work is or is not of value." 



But I have already said that the discovery of oxygen 

 was the most important discovery ever made in chemistry, 

 and I might have added, the most valuable. In what, then, 

 did its value consist? In the fact that it led to a more 

 intelligent working with all things chemical. Operations 



