In the year 1791 he communicated to the Royal Society his Analysis of the carbonic acid. M. Lavoisier had proved by decisive synthetic experiments that fixed air was a compound of oxygen and charcoal; but no one had yet resolved that gas into its simple elements. Mr. Tennant observing that phosphate of lime was not decomposed, when heated with charcoal, inferred that the joint attractions of phosphorus for oxygen, and of phosphoric acid for lime, exceeded those of charcoal for oxygen, and of carbonic acid for lime; and consequently that phosphorus and heated marble, when made to act on each other, would be resolved into phosphate of lime and charcoal. The correctness of this reasoning was fully justified by the event; and the result of the experiment was not merely the analysis of the carbonic acid, which was the immediate object of the investigation, but the discovery of a new compound, consisting of phosphorus and lime, possessed of several curious properties.

The ingenuity and elegance of this experiment established Mr. Tennant's reputation as a chemist; and there being at the close of that year the prospect of a vacancy in the Jacksonian Professorship at Cambridge by the resignation of Dr. Milner, he was prevailed upon by his friends to become a candidate for that situation; but desisted from the pursuit on finding that he had no reasonable prospect of success.

In the year 1792 he again visited the Continent, with the intention of travelling through France to Italy, and arrived at Paris not long before the memorable 10th of August. He hardly recognized some of his old scientific friends, now become Members of the Legislative Assembly, and deeply implicated in the revolutionary politics of the times. From various circumstances, he anticipated some great and speedy convulsion, and was fortunate enough to quit Paris on the 9th of August, before the flame actually broke

out.

In passing through Switzerland he visited Mr. Gibbon, at Lausanne, and was much struck with his powers of conversation, and the sagacity of his remarks on the course and progress of the French revolution, and on the probable issue of the invasion of France by the allied armies under the Duke of Brunswick.

In Italy he was delighted with the softness and beauty of the climate, and the luxuriance of the vegetation, and was astonished by the wonders of ancient and modern art at Rome and Florence. He had hitherto been somewhat sceptical as to the degree of merit really belonging to the great masters in painting, whose fame he had supposed to be founded principally upon exaggeration. But he was converted from this error by the great works of Raphael and Correggio; and of the former, more especially, of these distinguished artists, he was ever afterwards a devoted and enthusiastic admirer.

He returned from Italy through a part of Germany, and was much amused with the mixture of science and credulity which he

found in some of the German chemists. The philosopher's stone was spoken of with respect; and he received from a man of science and character an introduction to a person who was reputed to be in possession of that treasure. Mr. Tennant used to relate with his own peculiar, humour the solemnity with which he was received by this person; with whom he conversed in Latin, and who exhibited to him the mysterious powder, enlarging upon its transcendent qualities with much pomp, and in flowing and sonorous periods.

On his return through Paris in the latter end of 1792, or beginning of 1793, he was deeply impressed with the gloom and desolation arising from the system of terror then beginning to prevail in that capital; a particular instance of which deserves, on several accounts, to be recorded.

Among his philosophical acquaintance at Paris, there was one distinguished by his simplicity and moderation, of whose excellent qualities he always expressed a high value. This was M. Delametherie, editor of the Journal de Physique. Upon calling at his house, Mr. Tennant found the doors and windows closed, as if the owner was absent. Being at length admitted, he found his friend sitting in a back room, by candle-light, and with shutters closed, in the middle of the day. On his departure, after a hurried and anxious conversation, his friend conjured him not to come again, as the knowledge of his being there might be attended with serious consequences to them both. It should be mentioned, to the honour of this Gentleman, that through all the inquisitions of the revolu tion he preserved for his friend property of considerable value, which Mr. Tennant had entrusted to his care.

Soon after Mr. T.'s return from the Continent, he took chambers in the Temple, which continued from that time to be his established place of residence; and for many years his society was very much limited to a small circle of friends. Owing to accidental circumstances, his early connections had been much more formed among students of the law than among those of the profession which he had originally designed to pursue, but to which he was gradually becoming more and more indifferent. He had not, however, as yet abandoned the intention of practising medicine; and for several years applied himself to the cultivation of the studies connected with that science, and attended regularly at some of the principal London hospitals. Of his industry and perseverance in this course sufficient proofs exist in the medical notes and memoranda now found among his papers; and it is well known to some of his friends that he had also read with great attention most of the standard books in that science. Among these he always spoke of the works of Sydenham (with reference to the age in which they were produced) in terms of the highest admiration. Curiosity had also led him to examine the principal medical writers of antiquity, whose merits and defects he correctly appreciated, and upon whom he had made many curious and valuable remarks. He had taken a

comprehensive view of the origin and progress of medicine, and of the various medical theories and opinions which have prevailed in different ages and countries; and seemed on this account peculiarly well qualified (independently of his practical knowledge) to have written a philosophical history of the science.

But the question was very different, how far he was well qualified to practise medicine with advantage as a lucrative profession; and the period was now arrived, when this point was to be determined. Several of his friends, although very doubtful as to the ultimate success of the measure which they recommended, were yet extremely desirous that he should try the effects of a regular profession; which they considered as affording the best prospect of giving an useful direction to his talents, and fixing his desultory habits. In deference chiefly to their opinion, he took his degree of Doctor of Physic at Cambridge in the year 1796, and for some time had serious thoughts of commencing medical practice. But, after some hesitation, he wisely relinquished a design, which, whether successful or not, was unlikely to contribute to his happiness. His desires were moderate, and his private fortune exempted him from the necessity of following any employment as the means of subsistence. He was at liberty, therefore, to indulge his own inclinations; and his careless, independent habits of life, no less than the general cast of his character and understanding, rendered him altogether averse to the drudgery and restraints of a profession. It may be observed also as a circumstance by which he was undoubtedly much influenced in adopting this resolution, that he had suffered very greatly, during his attendance at the hospitals, in consequence of the acute and painful emotions he had constantly experienced from those sights of hopeless misery which he had so often occasion to witness. He justly apprehended that the frequent recurrence of such scenes, unavoidable in medical practice, would be destructive of his comfort and happiness.

The keen and exquisite sensibility, from which these feelings originated, was a striking feature in Mr. Tennant's character, and not only gave a colour to many of his opinions, but powerfully influenced his conduct. An instance of his practical benevolence, derived from this principle, happened about this period, which may perhaps deserve to be mentioned. He had a steward in the country in whom he had long placed implicit confidence, and who was considerably indebted to him. In consequence of this man's becoming embarrassed in his circumstances, Mr. T. went into the country, in order to look into his accounts. A time and place were appointed for him to produce his books, and shew the extent of the deficiency; but the unfortunate steward felt himself unequal to the task of such an explanation; and in a fit of despair put an end to his own existence. Touched by this melancholy event, Mr. T. used his utmost exertions for the relief and protection of the family whom he had left, and not only forgave them the debt, but afforded them pecuniary assistance, and continued ever afterwards to be their friend and benefactor,

During the course of the year 1796 Mr. Tennant communicated to the Royal Society his paper on the nature of the Diamond. Sir Isaac Newton had conjectured that this body was inflammable, as was afterwards proved by the experiments of the Duke of Tuscany and of Messrs. Darcet and Rouelle. M. Lavoisier effected its combustion by means of a lens, in close vessels, and obtained from it a gas, which precipitated chalk from lime-water. But this was at an early period of pneumatic chemistry; and although he concluded that the gas was fixed air, yet he did not consider the analogy between charcoal and the diamond as very intimate, but as depending only on their common property of being combustible. The merit of completely ascertaining the nature of this substance was therefore reserved for Mr. Tennant. He succeeded in burning the diamond when reduced to powder, by heating it with nitre in a gold tube. A solution of the alkaline salt was then poured into liquid muriate of lime; and the quantity of carbonic acid which had been generated was inferred from the weight of the precipitate, which was found to consist of carbonate of lime.

From experiments made upon minute quantities of diamond powder, not exceeding 24 grains, he shewed, by comparing them with Lavoisier's experiments on charcoal, that equal weights of diamond and charcoal yield equal quantities of fixed air, and that fixed air contains between 27 and 27.8 per cent. of diamond; results which very nearly agreed with those of M. Lavoisier, and were subsequently confirmed by the investigations of Messrs. Allen and Pepys.

In the course of his investigation of the diamond, Mr. Tennant observed that gold and platina were corroded and dissolved by heated nitre; and that on the addition of water to the salt, the metals, owing to the presence of nitrite of potash, were in a great measure precipitated. These appearances, together with some peculiar properties of the nitrous solutions of gold, were the subject of a further communication to the Royal Society in 1797.

It is worthy of remark, that Mr. Tennant had ascertained the true nature of the diamond some years before he made the above communication to the Royal Society. In conversing about this time with a particular friend, whom he was attending with affectionate care during a lingering illness in the spring of 1796, he happened to mention the fact of this discovery. His friend, who had often lamented Mr. T.'s habits of procrastination, urged him to lose no time in making his experiment public; and it was in consequence of these entreaties that the paper on the diamond was produced. A still more remarkable example of the same indolence or inattention occurred in the case before alluded to of the paper on double distillation, communicated to the Royal Society in 1814, the substance of which he had mentioned to some of his friends during his residence at Cambridge.

These facts are memorable and instructive instances of the strength and weakness of Mr. Tennant's mind. 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 Mr. Tennant's mind cooperated, 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 the 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. It is yet to be ascertained, by a careful examination of his papers, whether any fragments of this great body of knowledge still remain, which can now be converted to use; whether any of his various discoveries not hitherto made public (some of which unquestionably were important) are capable of being traced out and understood from the loose and imperfect hints which his scattered notes may furnish. But there is too much reason to believe that the far greater part of them existed only in the mind of their author, and that with him they have unfortunately perished!

(To be continued.)

ARTICLE II.

Account of a Toad found in the Trunk of a Beech.
By Thomas Lauder Dick, Esq.

SIR,

(To Dr. Thomson.)

In your Journal for this month, which has just reached me, I observe some queries have been proposed relative to toads found in rocks and trees. I agree with you, that in every such instance some fissure will be found communicating with the external air, nor have I ever heard of any well-authenticated case to the contrary. I am led to trouble you with this, not with any view of throwing light on