It was the fortune of this eminent philosopher, in the course of a long, uncompromising advocacy of his own views of truth, to become prominently engaged in controversy on those two great sources of discord, religion and politics. He was grossly maltreated by those who disapproved of his doctrines; and, as the natural consequence, he was regarded with warm, not to say immoderate, admiration by his friends. His opinions, however, were the result of patient inquiry, instituted and pursued, as we believe, with a sincere desire to arrive at truth; and therefore he is entitled to be treated with respect, even by those who think his opinions of pernicious tendency. A good life of such a man can hardly satisfy both friends and enemies. It is, however, as a man of science, not as a party disputant, that Priestley is entitled to a place here; and we shall therefore hold ourselves excused from entering at length into his political or theological controversies.

Joseph Priestley was born at Fieldhead, near Leeds, March 13, 1733, O.S. His father was of middle rank, engaged in the woollen manufactures of the neighbourhood. His mother died while he was still a child: but this loss was alleviated by the kindness of his paternal aunt, who undertook the care of his education from the time that he was nine years old. He underwent some disadvantage, in being shifted about from one tutor to another; but being of a studious turn, he made considerable progress in the study of ancient and modern languages, Asiatic as well as European, of mathematics, metaphysics, and other branches of learning; so that he was found to be unusually well informed, on his admission at the Dissenting Academy at Daventry, in 1752. His father and his aunt were Calvinistic Dissenters, and Priestley was brought up in an unusually strict observance of all the external duties of religion. He acknowledges in his memoirs an obligation to this course of life, as having early given him a serious turn of mind, but without recommending a similar course for general adoption. As was natural, he imbibed the principles of Calvinism; and suffered at one time severe uneasiness, because he could not realize in his mind those feelings which he had been taught to consider as the index of salvation. This we mention, because it shows that his early prepossessions were diametrically opposed to that system of religion to which he ultimately worked his way.

For three years Priestley continued at Daventry, labouring sedulously in studying to qualify himself for the ministry. At the end of that time, he accepted an invitation to become assistant preacher to a dissenting congregation at Needham Market, near Ipswich. His residence there, a period of three years more, was one of considerable want and difficulty. His stipulated salary amounted only to 40l., and was so ill paid, that his receipts generally fell short of 30l.: insomuch that, without occasional assistance, procured from different charities by his friends, he could scarcely have subsisted. This deficiency arose partly from the poverty of the congregation, partly from his own unpopularity. His religious views, which, during his abode at Daventry, had changed to Arianism, did not accord with those of his hearers; and he laboured under an impediment of speech. Yet, notwithstanding these unfavourable circumstances, he says, “I was far from being unhappy at Needham. I firmly believed that a wise Providence was disposing every thing for the best, and I applied with great assiduity to my studies, which were classical, mathematical, and theological. These required but few books. As to experimental philosophy, I had always cultivated an acquaintance with it, but I had not the means of prosecuting it.” The result of his theological studies was a still more decided rejection of the doctrines in which he had been brought up In his own words, “I had become, in consequence of much pains and thought, persuaded of the falsity of the doctrine of atonement, of the inspiration of the authors of the books of scripture as writers, and of all idea of supernatural influence, except for the purpose of miracles. But I was still an Arian, having never turned my attention to the Socinian doctrine, and contenting myself with seeing the absurdity of the Trinitarian system.”

Priestley’s situation was somewhat improved by an invitation to Nantwich, in Cheshire, in 1758. He remained there for three years, engaged in the double duty of preaching and keeping a school; and then accepted an appointment as tutor of languages in the Dissenting Academy newly established at Warrington. Not confining himself to the strict letter of his duties, he composed and delivered lectures on the theory of language, oratory, and criticism; on history in general, and on the history, laws, and constitution of England. It is a remarkable instance of his versatility and activity of mind, that, in addition to this extensive course of study, he undertook to write his History of Electricity, a subject with which he then was little acquainted, and finished it within a year, though in the course of the work he had been led into a large field of original experiments. After a residence of six years, the situation affording him a bare livelihood, he removed to Leeds, and took the charge of Mill Hill Chapel, in September, 1767.

At Leeds, Priestley resided for another period of six years, actively employed in clerical and scientific labours. Here his experiments on fixed air were undertaken, and published. He undertook a History of Discoveries relating to Vision, Light, and Colours, as part of a projected history of all the branches of experimental philosophy; but the sale of this portion was discouraging, and he abandoned the rest of the undertaking. He also published his well-known Chart of History, and wrote an Essay on Government, with other pieces, in addition to a great number of religious pamphlets. These various pursuits, with occasional visits to London, made him well known to literary men; and, by the friendship of Dr. Price, he was recommended to the Earl of Shelburne, as well qualified to fill the station of a literary companion and friend. In consequence, he removed to Calne in Wiltshire, close to that nobleman’s seat, Bowood. Nominally filling the office of librarian, and treated by Lord Shelburne with uniform respect and kindness, he had access to the best society, both at Bowood and in London: he also had the advantage of foreign travel. But at length a coldness grew up on the part of his patron; and at the end of seven years the connection was dissolved. By the terms of his agreement, Dr. Priestley became entitled to an annuity of 150l., which was punctually paid. Each party bore testimony to the honourable conduct of the other. The cause of this estrangement never was avowed; but it is probable that the boldness with which Priestley wrote in support of his peculiar metaphysical and religious doctrines may have displeased Lord Shelburne.

Induced by motives of family connection, Dr. Priestley now took up his residence at Birmingham. Local convenience and the society of various distinguished men, among whom James Watt was pre-eminent, rendered that town peculiarly suitable to his scientific pursuits, which, however, were never suffered to occupy him to the exclusion of theology. He undertook the ministry of a chapel. He revived the Theological Repository, which had been commenced and discontinued at Leeds. He composed and published his History of the Corruptions of Christianity. This work involved him in a well-known controversy with Dr. Horsley, who is commonly said to have owed his bishopric to his exertions in it. Priestley pursued the dispute in a history of early opinions concerning Jesus Christ; and for some time he wrote an annual pamphlet in answer to the attacks on Unitarianism. His intimate friend, Dr. Price, was the most distinguished among his opponents, and their controversy was carried on with eminent decency and candour. It was published in 1778, entitled “A free Discussion of the Doctrines of Materialism and Necessity, in a Correspondence between Dr. Price and Dr. Priestley, &c.” The Socinian tenets of the latter were again advocated in his General History of the Christian Church to the Fall of the Western Empire. These active labours in the field of controversy, backed by his general reputation, caused Priestley to be regarded as the leading person among the Dissenters, a body at that time distrusted by the government, and disliked by a large portion of their fellow-countrymen. The agitation of the repeal of the Test Act increased the prejudice against them, while it gave Priestley a fresh motive for exertion. Loud was the outcry, and bitter the hatred of the “Church and King” party. One of the clergy of Birmingham attacked him from the pulpit. To him and to another he replied in a series of Familiar Letters to the Inhabitants of Birmingham. At length party rage grew so high, that a meeting (at which Priestley was not present) being held by some persons, who looked favourably on the commencement of the French Revolution, July 14, 1791, to celebrate the anniversary of the destruction of the Bastile, the house in which they assembled was attacked by an infuriated mob. Dr. Priestley’s meeting-house and dwelling-house were the next objects of outrage; and the latter, with his valuable library, philosophical apparatus, papers, &c., was destroyed. The houses of several other Dissenters were more or less injured. He recovered a certain compensation for his losses; but the sum awarded, according to his statement, fell two thousand pounds short of their real amount. The liberality of his friends, however, more than made up the pecuniary deficiency. The French testified a warm sense of his ill-usage; and on the meeting of the National Convention, several of the departments invited him to become a member of it. This compliment he wisely declined.

Birmingham was no longer a pleasant, nor even a safe abode for the philosopher. He removed to Hackney, where the congregation of Dr. Price soon invited him to become the successor of his deceased friend. By degrees he replaced his philosophical instruments, and resumed his studies, hoping to finish his life without more removals. But as the French Revolution advanced, and political dissension in England ran higher and higher, his situation grew more unpleasant, and, in his estimation, more dangerous. He found himself shunned at the meetings of the Royal Society, and he ceased to attend them; he was harassed by threats and insults; he believed the violence of the high church party against him to be on the increase; he saw oppressive political prosecutions instituted against others, and thought himself a likely person to be marked for ruin. Above all, he found the evil repute into which he had fallen an effectual bar to the favourable establishment of his sons in England; and when they were gone to seek their fortunes in America, he resolved to follow them. He landed at New York in June, 1794, and shortly after settled at Northumberland, a town about one hundred and thirty miles N. W. of Philadelphia. There rejecting more than one advantageous offer of situations in the University of Philadelphia, he spent the remainder of life, continuing to the last his philosophical and theological studies. The chief fruit of these latter years was his General History of the Christian Church, in four volumes. After a gradual decline of strength, he died, February 6, 1804.

The private character of Priestley was such as to command respect. Modest, benevolent, pious, of studious and retired habits and unimpeached morals, the worst his enemies had to say of him was, that he taught heresy, and was an enemy of the established order of things. His works, not including those on scientific subjects, have recently been edited by Mr. Rutt, in twenty-five volumes 8vo., the first of which contains his own memoirs, illustrated by notes by the editor, and very numerous letters; and a catalogue of his publications in the order in which they appeared. The same memoirs, written by himself, in an unpretending and dispassionate style, and continued down to the author’s death, by his son Joseph Priestley, appeared in 1805, with an appendix, containing notices of his works and opinions. With respect to his philosophical merits, the eloge pronounced on him by Cuvier to the Institute, of which Priestley was an associate, in 1805, will command attention, like every production of its distinguished author.

In the space to which we are restricted, it will be impossible to give an adequate idea of the vast importance of Dr. Priestley’s chemical discoveries: they are justly regarded as forming the basis of our knowledge of pneumatic chemistry, and indeed of the science in general; for upon one of them alone, that of oxygen gas, is founded our acquaintance with the nature of air, earth, and water, and the same discovery has served also to explain the action of fire.

Dr. Priestley’s residence at Leeds was near a brewery; and his first pneumatic experiments were made on the carbonic acid gas, or fixed air, largely generated during fermentation. Gradually pursuing the subject, he examined various other aËriform bodies, and submitted to experiment numerous substances which were convertible into, or capable of yielding, air. These investigations led him to the discovery of new gaseous bodies, both elementary and compound. So little cultivated had been the field in which he commenced his researches, that he was under the necessity of imagining and constructing new instruments, in order to carry them on. To his inventive genius chemistry is indebted for the pneumatic trough, the method of receiving and retaining gases over mercury, and the process of combining and decomposing them by electricity. “The very implements,” Dr. Henry remarks, in his Estimate of the Philosophical Character of Dr. Priestley, “with which he was to work were, for the most part, to be invented; and of the merits of those which he did invent, it is a sufficient proof that they continue in use to this day, with no very important modification. All his contrivances for collecting, transferring, and preserving different kinds of air, and for submitting those airs to the action of solid and liquid substances, were exceedingly simple, beautiful, and effectual. They were chiefly, too, the work of his own hands, or were constructed under his directions by unskilled persons.” Dr. Priestley’s first publication on pneumatic chemistry appeared in 1772; it was called “Directions for impregnating Water with fixed Air,” &c. &c. In this work he proposed the use of a condensing engine for the purpose of causing the water to dissolve a larger quantity of the gas, and thus to prepare artificial mineral waters: this plan, it is well known, is now practised to a great extent. In the Philosophical Transactions for 1772, he announced the discovery that air, which had been vitiated by respiration or the burning of candles, was restored by the vegetation of plants; that air exposed to a mixture of sulphur and iron filings, as had previously been done by Hales, was diminished by about one-fourth or one-fifth in bulk, and that the residual air was lighter than atmospheric air, and noxious to animals. This diminished air he afterwards called phlogisticated air; it is now named azotic, or nitrogen gas. The discovery of this fluid is generally attributed to Dr. Rutherford, who, in his treatise “De AËre Mephitico,” also published in 1772, mentioned a few of its properties without giving it any name. As Dr. Priestley’s papers were read before the Royal Society so early as in March, it is not improbable that he was the first discoverer of the gas in question. In 1774 appeared the first of three volumes, entitled “Experiments and Observations on different kinds of Air;” and these were followed by three more, entitled “Experiments and Observations relating to various Branches of Natural Philosophy, with a continuation of the Observations on Air:” the last of these was published in 1786. This work contains a series of experiments, unrivalled for their number, novelty, and importance.

Dr. Priestley’s greatest discovery, that of oxygen gas, which he called dephlogisticated air, was made on the 1st of August, 1774, and announced in the Philosophical Transactions for 1775. This gas he first procured from red oxide of mercury, and afterwards from red oxide of lead, and several other substances.

In 1776 Dr. Priestley’s Observations on Respiration were read before the Royal Society. In these he showed that atmospheric air, during inspiration, was diminished in quantity, and deteriorated in quality, by the action of the blood upon it through the blood-vessels of the lungs. He also proved that gases have the power of acting through bladders, and one of his latest papers was on this curious subject: it appeared in the fifth volume of the American Philosophical Transactions, and seems to have been completely overlooked by later experimenters on the same subject. Another of his early and important observations related to the permanent mixture of gases of different densities, in cases in which they do not combine; and he cited this circumstance to account for the perfect mixture of the two gases which form the atmosphere, and which are well known to be of different densities.

In addition to oxygen gas, already mentioned, Dr. Priestley also discovered muriatic acid gas, sulphurous acid gas, fluoric acid gas, nitrous oxide gas, ammoniacal gas, and carbonic oxide gas; but he entirely mistook the nature of the last-mentioned body. He also showed that muriatic acid gas and ammoniacal gas, when mixed, condense into solid sal ammoniac. He must also have obtained chlorine gas, but it escaped his notice, because, being received over mercury, it quickly combined with it. Hydrogen gas and carbonic acid gas were known before his time; but his experiments upon them greatly extended our acquaintance with their properties. Nitrous gas, barely discovered by Dr. Hales, was first investigated by Priestley, and applied by him to eudiometry, a most important branch of chemical science originating with himself.

In 1778, he pursued his experiments on the property of vegetables growing in the light, to renovate impure air, and on the use of vegetation in this part of the economy of nature. Chemistry is also indebted to him for the method of decomposing metallic oxides by means of hydrogen gas, and for noticing that this gas has the property of dissolving iron. He observed also that lime is less soluble in hot than cold water; and that when a solution of lime in cold water is heated, part of the lime is deposited.

In the first volume of his work on air (p. 278), Dr. Priestley has anticipated the idea of Dr. Arnott and Sir J. F. W. Herschel, that electricity, acting on the brain and nerves, may excite muscular action.

Dr. Henry, in the memoir already quoted, has remarked, that facts are to be met with in various parts of Dr. Priestley’s works that might have given him a hint of the law, since unfolded by the sagacity of M. Gay-Lussac, “that gaseous substances combine in definite volumes.” From the same memoir we extract the following observations, in conclusion of this short account of Dr. Priestley’s scientific labours:—“He greatly enlarged our knowledge of the important class of metals, and traced out many of their most interesting relations to oxygen and to acids. He unfolded, and illustrated by simple and beautiful experiments, distinct views of combustion; of the respiration of animals, both of the inferior and higher classes; of the changes produced in organized bodies by putrefaction, and of the causes that accelerate or retard that process; of the importance of azote as the characteristic ingredient of animal substances, observable by the action of dilute nitric acid on muscle and tendon; of the functions and economy of living vegetables; and of the relations and subserviency which exist between the animal and vegetable kingdoms.”