A Century of Science 3 



phlogiston might weigh less than nothing, or, in 

 other words, might be endowed with a positive at- 

 tribute of levity, so that to subtract it from a 

 body would increase the weight of the body. This 

 was a truly shifty method of reasoning, in which 

 your phlogiston, with its plus sign to-day and its 

 minus sign to-morrow, exhibited a skill in facing 

 both ways like that of an American candidate for 

 public office. 



Into the structure of false science that had been 

 reared upon these misconceptions Dr. Priestley's 

 discovery of oxygen came like a bombshell. As in 

 so many other like cases, the discovery was destined 

 to come at about that time ; it was made again 

 three years afterward by the Swedish chemist 

 Scheele, without knowing what Priestley had done. 

 The study of oxygen soon pointed to the conclusion 

 that, whatever may escape during combustion, oxy- 

 gen is always united with the burning substance. 

 Then came Lavoisier with his balance, and proved 

 that whenever a thing burns it combines with 

 Priestley's oxygen, and the weight of the resulting 

 product is equal to the weight of the substance 

 burned plus the weight of oxygen abstracted from 

 the air. Thus combustion is simply union with 

 oxygen, and nothing escapes. No room was left 

 for phlogiston. Men's thoughts were dephlogis- 



