A CENTURY OF SCIENCE 



A CENTURY OF SCIENCE 1 



IN the course of the year 1774 Dr. Priestley 

 found that by heating red precipitate, or what we 

 now call red oxide of mercury, a gas was obtained, 

 which he called " dephlogisticated air," or, in other 

 words, air deprived of phlogiston, and therefore 

 incombustible. This incombustible air was oxygen, 

 and such was man's first introduction to the 

 mighty element that makes one fifth of the atmo- 

 sphere in volume and eight ninths of the ocean by 

 weight, besides forming one half of the earth's 

 solid crust, and supporting all fire and all life. 

 I know of nothing which can reveal to us with 

 such startling vividness the extent of the gulf 

 which the human mind has traversed within little 

 more than a hundred years. It is scarcely possi- 

 ble to put ourselves back into the frame of mind 



1 An address delivered in the First Unitarian Church of Phila- 

 delphia, May 13, 1896, at the celebration of the one hundredth an- 

 niversary of its founding, under the lead of the illustrious Dr. 

 Priestley. 



