and be less apt to be offended when the performances they hear are but indifferent. In 1761 he was invited to Warrington, as "tutor in the languages" in the Dissenting Academy in that town. Here he taught Latin, Greek, Hebrew, French, and Italian; and delivered courses of lectures on Logic, on Elocution, on the Theory of Language, on Oratory and Criticism, on History and General Policy, on Civil Law, and on Anatomy. About this time, too, he made the friendship of Benjamin Franklin-a friendship which constitutes a turning-point in Priestley's career, for Franklin encouraged his leaning towards philosophical pursuits, warmly recommending him to undertake his proposed History of Electricity, and furnishing him with books for the purpose. In connection with this work, he made a number of original observations in electricity, on account of which the book was favourably received; its author was made a Fellow of the Royal Society, and a Doctor of Laws of Edinburgh University. Priestley by this time was married, but seeing no prospect of providing for his family at Warrington, he accepted an invitation to take charge of a congregation in Leeds, and thither he removed in 1767. Having leisure, he redoubled his attention to experimental philosophy, and began that brilliant series of discoveries by which others were to accomplish the overthrow of that system of chemical philosophy of which he considered himself the special champion. "But," writes Priestley, "the only person in Leeds who gave much attention to my experiments was Mr. Hey, a surgeon. When I left Leeds he begged off me the earthen trough in which I had made all my experiments on air while I was there. It was such an one as is there commonly used for washing linen."

.

In 1772 Lord Shelburne wished for a "literary

companion," and Priestley was induced to accept the office by the offer of a good salary, a house and other appointments, together with an annuity at the end of the engagement. Fortunately for science, his lordship had scarcely any duties for his literary companion to perform, and Priestley was thus able to give most of his time to the continuation of his chemical work. He remained with Lord Shelburne seven years.

He then settled in Birmingham, and accepted the charge of a congregation which he characterises as the most liberal in England. He was now nearly sixty years of age, free from embarrassment of every kind, and happy in the friendship of such men as Boulton and Watt, the engineers; Wedgwood the potter; Keir, Withering, Darwin, and the Galtons. He had ample leisure for his work, and no lack of encouragement and substantial help when needed. The picture of his life which he draws at this time indicates his serenity of mind and his sense of rest. He is thankful to that good Providence which always took more care of him than he ever took of himself, and he esteems it a singular happiness to have lived in an age and country in which he had been at full liberty both to investigate, and, by preaching and writing, to propagate religious truth. This calm, however, was but the presage of a great storm, and it burst over the old philosopher during the loud strife of party passion which agitated this country at the outbreak of the French Revolution. On the occasion of a public dinner on the anniversary of the taking of the Bastile, at which dinner Priestley was not present, and with which it does not appear that he had anything to do, a mob attacked and wrecked, in the name of "Church and King," the chapels and houses of the Dissenters in the town. The full fury of the rising

seemed to be concentrated upon Priestley, and he and his family barely escaped with their lives, leaving library, papers, and instruments to the tender mercies of the insane crowd, who speedily demolished what had been the labour and fruit of years. Priestley with difficulty got to London, but so uncertain was the temper of the time that his friends forcibly kept him in hiding for some weeks. His appeal for redress met with but a tardy acknowledgment, and the recompense which he eventually received was absurdly disproportionate to his disastrous experience of what Mr. Pitt was pleased to call "the effervescence of the public mind." His sons, disgusted with the justice which he received, left the country, and eventually settled in America. Although he himself was not without a position, for he was invited to minister to a large congregation at Hackney before he had been many months in London, and his friends vied with each other in rendering him help, his situation was still hazardous: his scientific brethren turned their backs upon him, his servants feared to remain with him, and the tradespeople declined to have his custom. At length he determined to follow his sons. Before he left he wrote these remarkable words: "I cannot refrain from repeating again, that I leave my native country with real regret, never expecting to find anywhere else society so suited to my disposition and habits, such friends as I have here (whose attachment has been more than a balance to all the abuse I have met with from others), and especially to replace one particular Christian friend, in whose absence I shall, for some time at least, find all the world a blank. Still less can I expect to resume my favourite pursuits with anything like the advantages I enjoy here. In leaving this country I also abandon a source of maintenance

which I can but ill bear to lose. I can, however, truly say that I leave it without any resentment or ill-will. On the contrary, I sincerely wish my countrymen all happiness; and when the time for reflection (which my absence may accelerate) shall come, they will, I am confident, do me more justice. They will be convinced that every suspicion they have been led to entertain to my disadvantage has been ill-founded, and that I have even some claim to their gratitude and esteem. In this case I shall look with satisfaction to the time when, if my life be prolonged, I may visit my friends in this country; and perhaps I may, notwithstanding my removal for the present, find a grave (as I believe is naturally the wish of every man) in the land that gave me birth." He never returned. His sons had settled at Northumberland, a little town placed in one of the most beautiful spots on the Susquehanna. Here, surrounding himself with books and taking but little interest in the politics of the country, he occupied himself to the last with philosophy and his beloved theology; steadily refusing to become naturalized, although the expediency of such a step was frequently pressed upon him, saying that "as he had been born and lived an Englishman he would die one, let what might be the consequence."

Priestley is mainly remembered by his theological controversies and his contributions to the history of pneumatic chemistry. I have nothing to tell you of his merits as a controversialist, except to say that some of his argumentative pieces are among the most forcible and best written of his literary productions. It is on his chemical work that his reputation will ultimately rest this will continue to hand down his name when all traces of his other labours are lost. He has frequently

been styled the Father of Pneumatic Chemistry; and although we may question the propriety of the appellation when we call to mind the labours of Van Helmont, of Boyle, and of Hales, there is no doubt that Priestley did more to extend our knowledge of gaseous bodies than any preceding or successive investigator.

Priestley was born just as Stahl, the author of what is known in the history of chemistry as the Phlogistic Theory, had run out his course. To this theory, handed down as it seemed to his especial keeping, Priestley unswervingly adhered. But, by a strange perversity of fate, the very discoveries which he brought forward as the strongest proofs of the soundness of the Phlogistic doctrine have conduced, perhaps more than any other set of facts, to its destruction. Let me attempt to give you some other notion of this Phlogistic Theory. A piece of wood burns: a piece of stone does not. Why is this? 66 Because," answers Stahl, "the wood contains a peculiar principle-the principle of inflammability: the stone does not. Coal, charcoal, wax, oil, phosphorus, sulphur-in short, all combustible bodies-contain this principle in common: to this principle (which, indeed, I regard as a material substance) I give the name of Phlogiston. I regard all combustible bodies, therefore, as compounds, and one of their constituents is this phlogiston: the differences which we observe in combustible substances depend partly upon the proportion of the phlogiston they contain, and partly upon the nature of the other constituents. When a body burns it parts with its phlogiston; and all the phenomena of combustion -the heat, the light, and the flame-are due to the violent expulsion of that substance. This phlogiston lies at the basis of all chemical change: all chemical reactions are so many manifestations of parts played by