muriatic acid, and pointed out easy methods of procuring them; he describes with exactness the most remarkable properties of each. He likewise pointed out the existence of carburetted hydrogen gas, though he made but few experiments to determine its nature. He also discovered protoxide of nitrogen, and, after he came to this country, carbonic-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. Cavendish's great discovery of the composition of nitric acid. His experiments on the influence of plants and animals upon the air were interesting 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 quarrelsome disposition, it would have been evinced in the numerous and changing relations with the people among whom 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 convictions 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, ending in violence and persecution, darkened the close of his life. The 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 society 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
