486 THE POPULAR SCIENCE MONTHLY, 



muriatic acid, and pointed out easy methods of i^rocuring them ; he de- 

 scribes with exactness the most remarkable properties of each. He 

 likewise j^ointed out the existence of carburetted hydrogen gas, though 

 he made but few experiments to determine its nature. He also dis- 

 covered protoxide of nitrogen, and, after he came to this country, car- 

 bonic-oxide gas. Though not strictly the discoverer of hydrogen, yet 

 his experiments on it were highly interesting, and contributed to the 

 progress of the science. Nitrogen had been previously discovered, but 

 we are indebted to him for a knowledge of most of its properties. To 

 him also we owe the knowledge of the fact that an acid is formed 

 when the electric sparks are made to pass for some time through a 

 given bulk of common air ; a fact which led afterward to Mr. Caven- 

 dish's great discovery of the composition of nitric acid. His experi- 

 ments on the influence of plants and animals uj^ou the air were inter- 

 esting and important. 



It has been said of Dr. Priestley that he was fond of controversy, 

 yet he never sought it, and, if he participated in it, it was generally 

 because it was thrust upon him, and he became the defendant rather 

 than the assailant. His discussions, so far as they depended upon 

 himself, were commonly carried on without anger, and he was never 

 malicious or even sarcastic, unless provoked. Had he been of a quar- 

 relsome disposition, it would have been evinced in the numerous and 

 changing relations with the people among wliom he lived, but he 

 never quitted a situation but with the sincere regrets of those among 

 whom he had dwelt, and with parting testimonies of their affectionate 

 approbation of his conduct. He was, however, a man of strong con- 

 victions upon subjects of the highest interest, and of great intellectual 

 force, and, what is still more important, he represented an unpopular 

 class and held opinions that were generally regarded in England with 

 detestation. These facts go far to explain the controversies in which 

 he was engaged, without attributing to him a love of disputation. 



It was while in Birmingham that he was drawn into conflict with 

 the established clergy of the place, which became embittered, and, end- 

 ing in violence and persecution, darkened the close of his life. Tlie 

 utmost that can be said in condemnation of Priestley at this time is, 

 that he expressed his opinions with a degree of freedom which, though 

 it would have been of little consequence at any former period, was ill- 

 suited to the temper of the times. We have seen that Dr. Priestley 

 had published an essay on the first principles of civil government. In 

 this he laid down as the foundation of his reasoning that " it must be 

 understood, whether it be expressed or not, that all people live in so- 

 ciety for their mutual advantage ; so that the good and happiness of 

 the members, that is the majority of the members of any state, is the 

 great standard by which every thing relating to that state must be 

 finally determined ; and, though it may be supposed that a body of 

 people may be bound by a voluntary resignation of all their rights to a 



