Smithson, a distinguished chemist, born at Selby in Yorkshire, 30th November 1761, was the only child of the Rev. Calvert Tennant, younger son of a respectable family in Wensley Dale, near Richmond, and vicar of Selby. His mother was Mary Daunt, daughter of a surgeon of that town. His father had been a fellow of St John's College, Cambridge, and began to teach his son Greek when he was only five years old. He had the misfortune to lose him four years after; and before he grew up, his mother also, while he was riding with her, was thrown from her horse and killed on the spot. He was sent, after his father's death, to different schools, at Seerton, Tadcaster, and Beverley. In these he was remembered as a boy retired in his manners, and somewhat melancholy, and indolent with respect to puerile amusements. He learned little at school, and may be considered as in a great measure self-educated; having been fond, almost as a child, of reading books of science, and of amusing himself with little experiments which he found described in them; and while he was at school at Tadcaster, he took great delight in attending a course of Walker's lectures on experimental philosophy which were given there. At Beverley he was under the care of Dr G. Croft, who had made himself known to the public by some controversial writings. Here he never entered much into the pursuits of his contemporaries, but profited by a good library belonging to the school; and among other books which he read with avidity was Sir Isaac Newton's Treatise on Optics.

He had entertained a great desire to complete his chemical studies under the immediate instruction of Dr Priestley, who was then enjoying deserved reputation for his recent experimental discoveries; but Dr Priestley's occupations did not permit him to undertake the task of directing his education, however agreeable it might have been to him to have assisted such a pupil. In the mean time he had not neglected his classics, but had acquired a sufficient knowledge of the learned languages to appreciate with cor- rect taste the beauties of the great writers of antiquity. Notwithstanding his admiration for Dr Priestley, he was an early convert to the antiphlogistic theory of chemistry; which, with all its errors, was still a material step in the advancement of science.

In 1781 he went to Edinburgh, with the view of qualifying himself for the profession of physic, and he had the advantage of attending Dr Black's lectures, which were then in great reputation. In October 1782, he entered as a pensioner of Christ's College, Cambridge, where he became intimately acquainted with the late Professor Harwood, who had been first a surgeon in India, but having lost, by the misconduct of an agent, the fortune which he had there acquired, submitted cheerfully to the toil of recommencing his career as a physician, though already past the middle age. His talents for conversation were such as were extremely likely to captivate a young man of superior discernment; and he formed a friendship with Tennant which continued uninterrupted throughout their lives. At Cambridge he studied a little of the mathematics in the works of Newton, but much more of chemistry and botany: he already began to exercise his inventive powers in an attempt to economize the consumption of fuel in distillation, which he did not make public until twenty years after, though he mentioned it at the time to some of his friends. He also occupied himself incessantly in general, and especially in political reading, though he was far from having the air of a student; but his rooms were always in confusion, from the mixture of heterogeneous materials that were accumulated in them. His residence at Cambridge was perhaps the happiest time of his life; his spirits unwarmed, his health unbroken, his feelings acute, and his conversation brilliant though simple and unaffected.

In the summer of 1784 he paid a visit to Denmark, to Sweden, and to Scheele, whose acquaintance extremely delighted him, and most of all from the simplicity of the apparatus that he employed in his researches. A year or two afterwards he went to France, and being taken ill at Paris, he was joined there by his friend Harwood, with whom he returned through Holland and the Netherlands, at the time when the bigoted people of the Low Countries were in insurrection against a philosophical despot, while Holland remained free and prosperous.

He was particularly intimate with Dr Milner, the master of Queen's College, and was recommended by his signature, together with those of Waring, Maskelyne, Jebb, and Watson, as a fellow of the Royal Society, into which he was admitted in January 1785. He removed, together with his friend Harwood, in December 1786, from Christ's College to Emanuel, and in 1788 he took the degree of bachelor of physic. In 1791 he communicated to the Royal Society his very interesting discovery of a mode of obtaining carbon from the carbonic acid. Having observed that charcoal did not decompose the phosphate of lime, he concluded that phosphorus ought to decompose the carbonate of lime; and the result fully justified his manner of reasoning.

He paid a third visit to the Continent in 1792, intending to pass through France into Italy, and arrived at Paris not long before the 10th of August; but he saw some indications of an impending convulsion, and was fortunate enough to quit Paris on the 9th. He visited Gibbon at Lausanne, and was much interested in the sagacity which this eminent writer displayed in his conversation. He proceeded to Rome and Florence, where he was fully impressed with all the admiration that he had been taught to anticipate for the treasures of ancient and modern art possessed by those cities; and in his return through Germany, he was greatly amused by the mixture of knowledge and credulity which he observed among the studious of that country. At Paris in 1793 he found everything enveloped in gloom and overwhelmed with terror. His friend Lametherie was alarmed by the visit which he paid him; but he had the integrity to preserve for him entire some property of considerable value, with which he had intrusted him.

Upon his arrival in London, Mr Tennant took chambers in the Temple, and was in the habit of living much with some of his early acquaintance, who had adopted the law as their profession; to his own he was in great measure indifferent, neither seeking to practise it, nor being well calculated to succeed greatly in it with the public, though he studied it with attention, and took pains to make himself master of its history and philosophy, being a particular admirer of Sydenham, when considered in relation to the age in which he lived. He took his degree of doctor of physic in 1796; and in the same year he gave the Royal Society a paper on the quantity of carbonic acid afforded by the diamond, which he measured by heating it with nitre, and obtaining a precipitate by the addition of muriate of lime; and he found that the diamond afforded no more carbonic acid than an equal weight of charcoal. A subsequent communication contained the result of his observations on the action of heated nitre on gold and platina.

The love of travelling appeared to be his predominant passion. In his travels, he studied not only the natural and political history of the countries which he saw, but also their languages, and the philosophy of their etymologies. He likewise observed the peculiarities of their agriculture; and, in 1797, he determined, after visiting an agricultural friend in Lincolnshire, to devote his attention to practical farming as a serious pursuit. He purchased some allotments of unclosed land in that neighbourhood, but he left the management of them chiefly to his friend, and afterwards made considerable additions to the property by further purchases. In 1798 or 1799, he bought a tract of newly enclosed land on the Mendip Hills, near Cheddar, where he built a house, and resided for some months every summer through the remainder of his life. These speculations, though their results were at first doubtful, yet succeeded remarkably well on the whole; more especially considering the benefit which his health derived from the travelling and the exercise that they rendered necessary; but they occupied too much of his attention, and of that time which might have been employed so much more to the advantage of the public, and to his own ultimate satisfaction.

In 1799 he gave the Royal Society a paper on the magnesian limestone, or dolomite, which he considers as rather a combination than an accidental mixture; and the forms of the crystals, as they have been determined by later observers, together with the laws of definite proportions, have tended to confirm this conjecture. He found that grain will scarcely germinate, and soon perishes, when sown in the neutral carbonate of magnesia. In 1802 he published his paper on emery, which he showed to be a substance similar to the corundum or adamantine spar of China, and not an ore of iron, as had been commonly supposed. In the month of July he was making some experiments on crude platina, when he discovered in it a singular dark powder, which was left undissolved by the nitro-muriatic acid, and which was also observed the next year by Messrs Descottis and Vauquelin. In 1804 Dr Tennant showed that the powder contained two new metals, which he named iridium and osmium; and he received the Copleian medal from the Royal Society in November, as an acknowledgment of the merit of his various chemical discoveries. In 1805 and 1806 he paid two successive visits to Ireland, by way of Scotland, one of them in company with Browne the traveller, for whom he had a high esteem, and to whom he suggested the observation of the temperature of boiling water as a mode of determining the heights of mountains; a method, however, which had been long before recommended by Achard and others. He became latterly more fond of general society than he had been in his earlier years, and he used to receive miscellaneous parties at his chambers, and to show them prints, and minerals, and novelties of various kinds. In 1812 he was persuaded to convert these mixed exhibitions into a more regular course of lectures, principally upon mineralogy, calculated especially for the ladies of his acquaintance, and which highly delighted all his audience: "Their attention was perpetually kept alive by the spirit and variety with which every topic was discussed, by anecdotes and quotations happily introduced, by the ornaments of a powerful but chastised imagination, and, above all, by a peculiar vein of pleasantry, at once original and delicate, with which he could animate and embellish the most unpromising subjects;" a circumstance which, though not of much immediate importance to the public, yet probably led him the more readily to accept the professorship at Cambridge, and would thus, if he had survived longer, have greatly extended the sphere of his utility.

In 1813 he delivered a lecture on mineralogy to the Geological Society, and gave them also an account of his analysis of a volcanic substance from the Lipari Islands, containing the boracic acid, which has since been examined on the spot by Dr Holland. In the month of May he was elected professor of chemistry in the university of Cambridge, all opposition having been withdrawn before the election. The following spring he gave his first and last course of lectures there. His introductory lecture still exists in manuscript, and is said to contain a masterly sketch of the history of the science. He communicated to the Royal Society, in 1814, a paper on the easiest mode of procuring potassium, and another on the economy of heat in distillation, proposing to heat a second boiler by the condensation of the steam of the first. In the spring and summer of this year he was occupied in searching for the origin of iodine, and he succeeded in detecting this substance in sea-water, by the test of its tarnishing the surface of leaf silver. One of the last services that he rendered the Royal Society, was in the capacity of a member of a committee which was formed in order to investigate, at the request of the government, the degree of danger that might attend the general introduction of gas-lights into the metropolis. He undertook, together with his friend Dr Wollaston, to make some experiments upon the inflammation of the gas, and they discovered conjointly the very important fact, that the gas contained in a small tube will not communicate the flame; a fact which, in the hands of Sir Humphry Davy, has been rendered productive of consequences so important to the public safety; although Sir Humphry having been abroad at the time of this investigation, and the report of the committee not having been then published, he had to rediscover this truth, and many more, in his most ingenious and successful researches.

It was early in the month of September that Dr Tennant went for the last time to France, being impatient to observe the changes which an eventful interval of twenty years had produced in that highly interesting country. He was greatly delighted with Lyon and Marseille; and, returning to Paris in November, he lingered there till February 1815. On the 15th of that month he arrived at Calais; on the 20th he went to Boulogne with Baron Bulow, in order to embark there. They did embark on the 22d, but were forced back by the wind, and meant to try again in the evening. In the mean time they took horses and went to see Bonaparte's Pillar, about a league off; and going off the road on their return, to look at a small fort, of which the drawbridge wanted a bolt, they were both thrown, with their horses, into the ditch. Bulow was only stunned, but Tennant's skull was so severely fractured, that he died an hour after.

His papers published in the Philosophical Transactions were eight in number. 1. On the Decomposition of Fixed Tennant Air, 1791, p. 182. 2. On the Nature of the Diamond, 1797, p. 123. 3. On the Action of Nitre upon Gold and Platina, p. 219. 4. On the different sorts of Lime used in Agriculture, 1799, p. 305. 5. On the Composition of Emery, 1802, p. 398. 6. On two Metals found in the Black Powder remaining after the Solution of Platina, 1804, p. 411. 7. On an easier Mode of procuring Potassium than that which is now adopted, 1814, p. 573. 8. On the Means of producing a double Distillation by the same Heat, p. 587.

9. The analysis of a Volcanic Substance containing the Boracic Acid appeared in the Transactions of the Geological Society, vol. I. 1811.

Dr Tennant was tall and slight in his person; his face was thin and his complexion light; he resembled a little the portraits of Locke; he was generally negligent in his dress, but, on the whole, agreeable in his appearance. He was distinguished for good sense, for quickness of perception, and for penetration; but, as his friend and biographer Mr Whishaw observes, in the admirably energetic sketch which he has given of his character, he was one of those who, to use the words of Dr Johnson, "without much labour have obtained a high reputation, and are mentioned with reverence rather for the possession than the exertion of uncommon abilities." "His curiosity and activity were incessant; he had a vigilance of observation which suffered nothing to escape him, and was continually gaining new information from a variety of interesting sources. But although the knowledge thus acquired was remarkable for its correctness, and complete for the purposes of its possessor, yet the industry and perseverance, by which it ought to have been embodied and made permanent for the benefit of others, were too often altogether wanting. The ardour and energy of Dr Tennant's mind co-operated unfortunately, in this respect, with his want of method and of systematic habits of application; since he was constantly pressing on to new discoveries, instead of arranging and bringing to perfection those which he had already made. His memory was a great storehouse of discoveries, and hints for discovery, of ascertained facts, probable conjectures, and ingenious trains of reasoning relative to the various important subjects upon which he had at any time been engaged. These he was continually treasuring up, with the intention of reducing them to order, and preparing them for use at a more convenient season. But that period rarely arrived. In the carelessness of intellectual wealth, he neglected those stores of knowledge which he had accumulated, and suffered them to remain useless and unproductive, till his attention was recalled to them, perhaps after a long course of years, by some new fact or discovery, some remark in conversation, or other accidental occurrence."

The effect of his peculiar cast of humour was heightened by a perfect gravity of countenance, a quiet familiar manner, and a characteristic simplicity of language. He was firmly attached to the general principles of freedom, being fully convinced "of their influence in promoting the wealth and happiness of nations; a due regard to these principles he considered as the only solid foundation of the most important blessings of social life, and as the peculiar cause of that distinguished superiority which our own country so happily enjoys among the nations of Europe." "The cheerful activity of a populous town, the improvements in the steam-engine, the great Galvanic experiments, and above all the novelty and extent of the prospects afforded by that revolution in chemical science which has illustrated our own age and country; these magnificent objects, when presented to Dr Tennant's mind, excited in him the liveliest emotions, and called for the most animated expressions of admiration and delight." "He thought himself passionate and irascible; and certainly his feelings were quick, but Tennessee, they were transitory." He possessed a strong sense of high honour, as well as of duty; and his liberality and humanity were evinced by some practical occurrences in which he had occasion to exercise them: his steward had defrauded him, and when the day of reckoning came, had destroyed himself: he not only forgave the debt, but provided also for the widow and her family.

"His amiable temper and unaffected desire of giving pleasure, no less than his superior knowledge and talents, had rendered him highly acceptable to a numerous and distinguished circle of society, by whom he was justly valued, and by whom his premature death was sincerely lamented. But the real extent of his private worth, the genuine simplicity and virtuous independence of his character, and the sincerity, warmth, and constancy of his friendship, can only be felt and estimated by those to whom he was long and intimately known, and to whom the recollection of his talents and virtues must always remain a pleasing though melancholy bond of union."