1 Antonii Bibliotheca Hispana, tom. ii. p. 354. 2 Anderson's pref. to Lesley's Defence, p. x. Leslie, Charles.

Leslie Adventu ad Regimen Provinciae Inferioris Germaniae. Per R. in Christo P. Joan. Leslieum, Episcopum Rossensem, Scotum. Subjicitur series vitae suae. Bruxelae, 1596, 8vo. This little work is reprinted in Anderson's Collections, vol. i. Of the account of the author's life, a translation is inserted in vol. iii.

6. A Discourse conteyninge a perfect Accomp given to the moste vertuous and excellent Princesse, Marie Queene of Scots, and her Nobility, by John Lesley, Bishop of Ross, Ambassador for her Highnes toward the Queene of England, of his whole Charge and Proceedings during the time of his Ambassage, from his entres in England in September 1568, to the 26th of March 1572. This account of the bishop's negotiations, which extends to 252 pages, was printed, for the first time, in Anderson's Collections relating to the History of Mary Queen of Scotland, vol. iii. Edinb. & Lond. 1727-8, 4 vols. 4to. As the language was Anglicized by Dr Good, it may be presumed that Lesley intended the work for immediate publication.

7. The History of Scotland, from the death of King James I in the year mccccxxxvi. to the year m.d.lxli. By John Lesley, Bishop of Ross. Edinburgh, 1830, 4to. This valuable relique was edited by Thomas Thomson, Esq. from a MS. belonging to the earl of Leven and Melville. Prefixed is a portrait of the author, copied from an old engraving, and representing him as a man of a dignified and sagacious aspect. Of his Scottish history the Latin is not a mere translation. "The readers of this volume," as the editor has remarked, "who may take the trouble of comparing it with the Latin version, will readily perceive that the alterations made by the author on his own original sketch do not consist merely in correction and enlargement; but that, in numerous instances, he has been induced to suppress or generalize those more minute details and domestic occurrences which he may have found less susceptible of that classic attire in which he was naturally ambitious of exhibiting his historical work. In this respect, the present publication may be found to contribute some few particulars to the materials of our national history; but a still higher value will probably be attached to it as a specimen of pure and vigorous composition, in his native language, by one of the most able and accomplished Scotchmen of the sixteenth century."

Leslie, Charles, was the second son of Dr John Leslie, bishop of Clogher, in Ireland, who was descended from an ancient family in the north of Scotland, and, being an admirable scholar, rose to the dignity of bishop of Orkney in his own country, whence he was, in the year 1633, translated to Raphoe, and afterwards, in 1661, to the see of Clogher, in Ireland.

Our author was born in Ireland, but in what year we have not learned. There is a ludicrous story, indeed, of his having been begotten in prison, and of his father having said that he hoped he would in consequence become the greatest scourge of the covenanters that Great Britain or Ireland had ever seen. This story, with all its circumstances, can scarcely be true; but we think it could not have been fabricated, had not Charles Leslie been born within a year of Cromwell's conquest of Ireland, when the good bishop, having sustained a siege in his castle of Raphoe, was some time kept in close confinement.

We are equally ignorant of the school where he was educated as of the year of his birth; but we know that he received his academical education in Trinity College, Dublin, where he took the degree of master of arts. In the year 1671, he lost his father, when he came over to England, and, entering himself in the temple, studied law for some years, but afterwards relinquished it for the study of divinity. In 1680 he was admitted into holy orders, and, in 1687, was made chancellor of Connor.

About this period he rendered himself particularly obnoxious to the Catholic party in Ireland, by his zealous opposition to them, which was thus called forth. Roger Car Boyle, bishop of Clogher, dying in 1687, Patrick Tyrrel was made Catholic bishop, and had the revenues of the see assigned him by King James. He set up a convent of friars in Monaghan, and, fixing his habitation there, held a public visitation of his clergy with great solemnity; when, some subtle logicians attending him, he challenged the Protestant clergy to a public disputation. Leslie undertook the task, and performed it to the satisfaction of the Protestants; though it happened, as it generally does at such contests, that both sides claimed the victory. He afterwards held another public disputation with two celebrated Catholic divines, in the church of Tyran, in the diocese of Armagh, before a very numerous assembly of persons of both religions; the issue of which was, that Mr John Stewart, a Catholic gentleman, renounced the church of Rome.

As the Catholics had got possession of an Episcopal see, they engrossed other offices also; and a Catholic high-sheriff was appointed for the county of Monaghan. This proceeding alarmed the gentlemen in that county, who, depending much on Leslie's knowledge as a justice of peace, repaired to him, then confined, by the gout, to his house. He told them, that it would be as illegal in them to permit the sheriff to act as it would be in him to attempt it. But they insisting that he should appear himself on the bench at the next quarter-sessions, and all promising to stand by him, he was carried thither with much difficulty and in great pain. When the sheriff appeared, and was taking his place, he was asked whether he was legally qualified; to which he answered smartly, "That he was of the king's own religion, and it was his majesty's will that he should be sheriff." Leslie replied, "that they were not inquiring into his majesty's religion, but whether he (the pretended sheriff) had qualified himself according to law, for acting as a proper officer; that the law was the king's will, and nothing else to be deemed such; that his subjects had no other way of knowing his will, but as it is revealed to them in his laws; and it must always be thought to continue so, till the contrary is notified to them in the same authentic manner." Upon this the bench unanimously agreed to commit the pretended sheriff, for his intrusion and arrogant contempt of the court. Leslie also committed some officers of the army which the Lord Tyrconnell raised, for offences.

By this spirited conduct Leslie acted like a sound divine and an upright magistrate; but though he thought himself authorized to resist the legal mandates of his sovereign, like many other great and good men, he distinguished between active and passive obedience, and felt not himself at liberty to transfer his allegiance from that sovereign to another. Refusing therefore to take the oaths to King William and Queen Mary, he was deprived of all his preferments; and in 1689 he removed with his family to England, where he published the following amongst other works: 1. Answer to Archbishop King's State of the Protestants in Ireland. 2. Cassandra, concerning the new Associations, &c. 1703, 4to. 3. Rehearsals; at first a weekly paper, published afterwards twice a week in a half-sheet, by way of a dialogue on the affairs of the times; begun in 1704, and continued for six or seven years. 4. The Wolf stripped of his Shepherd's Clothing, in Answer to Moderation a Virtue, 1704, 4to. The pamphlet it answers was written by James Owen. 5. The Bishop of Sarum's [Burnet's] proper Defence, from a Speech said to be spoken by him against occasional Conformity, 1704, 4to. 6. The new Association of those called Moderate Churchmen, &c. occasioned by a pamphlet entitled The Danger of Priestcraft, 1705, 4to. 7. The new Association, part ii. 1705, 4to. 8. The Principles of Dis- Mr Leslie having remained abroad from the year 1709 till 1721, returned that year to England, resolving, whatever the consequences might be, to die in his own country. Some of his friends having acquainted Lord Sunderland with his purpose, implored his protection for the good old man, which his lordship readily and generously promised. Mr Leslie had no sooner arrived in London, than a member of the House of Commons officiously waited on Lord Sunderland with the news, but met with such a reception from his lordship as the malice of his errand deserved. Our author then went over to Ireland, where he died, on the 13th of April 1722, at his own house at Glaslough, in the county of Monaghan.

His character may be summed up in a few words. Consummate learning, attended by the deepest humility, the strictest piety without the least tincture of moroseness, a conversation in the highest degree lively and spirited, yet to the last degree innocent, made him the delight of mankind; and has left what Dr Hickes says of him unquestionable, that he made more converts to sound faith and a holy life than any other man of his time.

A charge, however, has been brought against him, which, if well founded, must detract not only from his literary fame, but also from his personal integrity. The Short and Easy Method with the Deists is unquestionably his most valuable, and apparently his most original work; yet this work has been published in French amongst the works of the Abbé St Real, who died in 1692; and therefore it has been said, that unless it was published in English prior to that period, Charles Leslie must be considered as a shameless plagiarism.

The English work was certainly not published prior to the death of the Abbé St Real, for the first edition bears date the 17th of July 1697; and yet many reasons conspire to convince us that our countryman was no plagiarist. There is indeed a striking similarity between the English and the French works; but this is no complete proof that the one was copied from the other. The article Philology in this Encyclopedia, of which the late Dr Doig of Stirling was the author, was published the very same week in which Dr Vincent's dissertation on the Greek verb appeared. It was therefore impossible that either of these learned men, who till then were strangers to each other's names, could have stolen aught from the other; and yet Dr Vincent's derivation of the Greek verb bears as striking a resemblance to that of Dr Doig as the Abbé St Real's work does to that of Charles Leslie. In the article Miracle, too, the credibility of the gospel miracles is established by an argument, which the author certainly did not borrow from any one, and which the late Principal Campbell of Aberdeen considered as original; yet within half a year of the publication of that article, the credibility of the gospel miracles was treated in the very same manner by Dr Sayers, though there is in his dissertation complete internal evidence that he had not seen the article in this Encyclopedia. Further, the author of this sketch reviewed, in one of the Journals, the work of a friend, which was at the same time reviewed in another Journal which he never saw. Yet he was told by a friend, who was conversant in that kind of reading, and knew nothing of his concern with either Journal, that the book in question must, in both, have been reviewed by the same hand, because in both the same character was given of it in almost the very same words.

After these instances of apparent plagiarism, and which we know to be only apparent, has any man a right to say that Charles Leslie and the Abbé St Real might not have treated their subject in the way that they have done, without either borrowing from the other? The coincidence of arrangement and reasoning in two different works is indeed very surprising; but it is by no means so surprising as the coincidence of etymological deductions which appear in the writings of Drs Doig and Vincent. The divines reason from the acknowledged laws of human thought; the reasonings of the grammarians, with all deference to their superior learning, we cannot help considering as sometimes a little fanciful.

But this is not all that we have to urge on the subject. If there be plagiarism in the case, and the identity of titles looks very like it, it is infinitely more probable that the editor of St Real's works stole from Leslie, than that Leslie stole from St Real; unless it can be proved that the works of the abbe, and this work in particular, were published before the year 1697. At that period the English language was very little read or understood upon the Continent, whilst in Britain the French language was, by scholars, as generally understood as at present. Hence it is, that so many Frenchmen, and indeed foreigners of different nations, thought themselves safe in pilfering from the British philosophers; whilst there is not, in as far as we know, one well authenticated instance of a British philosopher appropriating to himself the discoveries of a foreigner. Is it then very improbable that the editor of the works of St Real would claim to his friend a celebrated tract, of which he knew the real author to be obnoxious to the government of his own country, and therefore not likely to have powerful friends to maintain his right?

But further, Dr Burnet, bishop of Sarum, was an excellent scholar, and well read, as every one knows, in the works of foreign divines. Is it conceivable, that this prelate, when smarting under the scourge of Leslie, would have let slip so favourable an opportunity of covering with disgrace his most formidable antagonist, had he known that antagonist to be guilty of plagiarism from the writings of the Abbé St Real? Let it be granted, however, that Burnet was a stranger to these writings and to this plagiarism; it can hardly be supposed that Le Clerc was likewise ignorant of them. Yet this author—when, for reasons best known to himself, he chose, in the year 1706, to depreciate the argument of Leslie's Short and Easy Method, and to traduce its author as ignorant of ancient history, and as having brought forward his four marks for no other purpose than to put the deceitful traditions of popery upon the same footing with the most authentic doctrines of the gospel—does not so much as insinuate that he had borrowed these marks from a popish abbe, though such a charge, could he have established it, would have served his purpose more than all his rude railings and invective. But there was no room for such a charge. In the second volume of the works of St Real, published in 1757, there is indeed a tract entitled Méthode Courte et Aisée pour combattre les Deistes; and there can be little doubt but that the publisher wished it to be considered as the work of his countryman. Unfortunately, however, for his design, a catalogue of the abbe's works is given in the first volume; and in that catalogue the Méthode Courte et Aisée is not mentioned.

We have dwelt thus long on The Short and Easy Method with the Deists, because it is one of the ablest works that ever was written in proof of the divine origin of the Jewish and Christian Scriptures; a work of which the high merit was acknowledged even by Lord Bolingbroke, and which, as is well known to theological scholars, Dr Conyers Middleton confessed to be unanswerable. If by men of science we should be thought to have spent our time well in vindicating the rights of some of our illustrious philosophers, to discoveries which have been unjustly claimed for the philosophers of Germany and France, we will not surely, by the friends of Christianity, be thought to have employed our time ill in vindicating Leslie's claim to this decisive argument in support of our holy religion.

Leslie, Sir John, Professor of Natural Philosophy in the University of Edinburgh, and author of several scientific works, inventions, and discoveries, of great celebrity, was born at the village of Largo, in the county of Fife, on the 16th of April 1766. If, in sketching the Life of this eminent person, we should happen to exceed the usual limits of our biographical notices, we can at least plead in excuse that we have done so in the case of one of the greatest benefactors of this Encyclopedia—one whose counsels led to not a few of the improvements which distinguish the later years of its history, and to whom it is indebted for many contributions, marked with the stamp of his vigorous and original powers. It is painful to us to recollect the number of similar claims to our attention. Too many illustrious contemporary benefactors have, like him, left us the mournful duty of preserving some memorials of their personal history, in the work which received from their co-operation its highest honours and proudest recommendations.

He was the son of humble, but, in their line of life, highly respectable parents, who lived to enjoy the celebrity of their son, and for whom he ever cherished that affection which formed a marked feature of his character, in regard to all the members of his family. His father, originally from the neighbourhood of St Andrews, lived for some time at Anstruther, but ultimately settled at Largo, as a joiner and cabinet-maker. His wife, Anne Carstairs, was a native of that place; and the subject of this article was the youngest child of their marriage. Though he attained in manhood a robust frame, he was, in early youth, of a very feeble constitution; so much so, that when sent, at four years of age, to a sort of school, kept by an old woman, who plied her wheel whilst teaching the alphabet, he was indulged with a separate stool, near the fire-place, which the dame set apart for the feeblest of her juvenile pupils. As long as he was permitted to monopolize this seat of honour, he seems to have been tolerably pleased with his situation; but being at length superseded by a younger, or more favoured pupil, he eloped from the school, hid himself for a day in some obscure corner, and, when obliged to come forth, obstinately refused to return to the tutelage of the ancient spinster. He was in consequence placed in another school, where he remained six months, and was taught writing and arithmetic; his father and his eldest brother, who appear to have possessed some knowledge of the elementary parts of mathematics, giving him, at the same time, his first lessons in that science. He was afterwards entered at a school in the neighbouring town of Leven, where Latin was taught; but his intense dislike, at this time, to that language, and his inability to walk and return daily a distance of three miles, induced his parents to discontinue his attendance, after a short trial of six weeks. Such was the brief and meagre curriculum which formed the whole training of the future mathematician and philosopher, previous to his being entered a student at the University of St Andrews! But we must not too hastily despatch this early period of his life, when his genius, working with its own inward resources, already began to attract observation.

The first person of any sort of distinction who noticed his precocious attainments, was Mr Oliphant, who became Minister of Largo about the time when the boy had reached his eleventh or twelfth year. Struck with the knowledge in mathematical and physical science which he displayed, the reverend gentleman kindly lent him some scientific books, with which he was but poorly provided; and he also strongly urged him to study Latin,—telling him, by way of showing the necessity of an immediate commencement, that it had cost himself seven years to acquire that language. This was the worst argument that could be urged to the young philosopher, who unhappily declared that he never would bestow half that time upon any language, and that he particularly disliked Latin. In this state of his knowledge and taste, he was, in his thirteenth year, sent to the University of St Andrews to study mathematics under Professor Vilant. On examination by the Professor, he was found already qualified for the second or senior class; and, at the close of the session, he obtained a prize. It is remembered, as a characteristic particular, that having previously discovered, in some of those antiquarian researches to which also he was early addicted, that it was not indispensable for students of the first year to wear a gown, he steadily refused, during this year, to exhibit himself in the accustomed academical habiliment.

This session proved a decisive one as to the course of his future studies. The Earl of Kinnoull, then Chancellor of the University, having been informed of his remarkable abilities, sent for his father, and proposed to him to defray the expense of his son's education, provided the father would agree to maintain him at college, with the view of qualifying him for the Church. The proposal was readily embraced; and the repugnance of the youth to apply himself to Latin was at length overcome, by making the permission to attend the Natural Philosophy class of next session,—the great object of his desire,—conditional on his agreeing to qualify himself, during the vacation, for attending also the Latin class. With this lure before him, he applied assiduously to his lessons, under the direction of a private teacher, and succeeded in fitting himself for admission into that class. No one could discover, in his after life, any traces of this early and vehement dislike to Latin; for though he ever held that the learned languages were suffered to engross too much attention in our system of education, and was by no means sparing of reprehension upon this subject,1 his own scholarship had become considerable; and indeed his writings manifest a more than ordinary degree of fondness for embellishing the conclusions of science with illustrations from the Greek and Latin Classics. He continued to the last to read them occasionally, particularly Lucretius, whose bold and imaginative philosophy, and splendid descriptions, were peculiarly adapted to his taste. He came also to be well versed in the theory of grammar; and his observations upon languages often evinced learning, as well as ingenuity.

His health, at the period above alluded to, was still so delicate that it became necessary to moderate and regulate his studious habits; but he succeeded, during his second session, in acquiring additional honours, and in attracting in a more marked degree the flattering attentions of the Chancellor, who kindly invited him to Dupplin Castle, where, notwithstanding the bashfulness of his manner, he contrived to impress the other visitors with a high opinion of his powers. About the same time, he became known to Mr Playfair, on occasion of a visit which the latter, amongst with the Reverend Dr Small, made to St Andrews. Dr Small's son was a fellow-student and companion of young Leslie, and hence his introduction to both these mathematicians. Mr Playfair was at this time parish minister of Lid, in Forfarshire. Here he was afterwards visited by his young acquaintance, neither of them then dreaming of that lot which was to place them, in succession, in two conspicuous Chairs of the University of Edinburgh, destined to derive from both additional lustre and recommendations. His visits to Mr Playfair were continued after the latter, in 1782, resigned his clerical charge, in order to superintend the education of the present Robert Ferguson, Esq. of Raith, and his brother Sir Ronald. It was in this way, we believe, that he first became known to these excellent and distinguished men, then youths of his own age; and the acquaintance, in after years, ripened into a warm and lasting friendship, alike honourable to both parties, and which formed one of the chief and most valued solaces of his life.

In 1783 or 1784, he quitted St Andrews, and proceeded to Edinburgh, with the intention of entering himself a student of Divinity in the metropolitan university. He was accompanied by a fellow-student, destined, like himself, to obtain a distinguished niche in the Temple of Science, James Ivory; and they lived together for some time. He never had any liking for the Church as a profession; and though he was formally entered at the Divinity Hall, he contrived to devote his first session to the sciences, particularly to Chemistry. In fact, he seems early to have relinquished all thoughts of the Church;—a resolution perhaps hastened by the death of his patron the Earl of Kinnoull, which took place soon after his removal to Edinburgh. He continued to study here till the close of the session of 1787; and, as is customary with students of greater ability and industry than means, devoted part of his time to private tuition. One of the young men whose studies he assisted was nearly related to, and became the heir of, Dr Adam Smith; a circumstance which he was accustomed to recollect with pleasure, as having made him known to that illustrious philosopher, who treated him kindly, and occasionally favoured him with directions as to his own pursuits. His first essay as an author must have been composed about the time of his leaving this university. It was a Paper On the Resolution of Indeterminate Problems, which was read to the Royal Society of Edinburgh by Mr Playfair, in 1788, and published in their Transactions.2

In this year, he was prevailed upon by two young students of the name of Randolph, and of the distinguished American family of that name, to accompany them, in capacity of tutor, to Virginia; and he accordingly left Scotland amongst with them. They arrived at the place of their destination in the beginning of November; and his time afterwards seems to have passed both agreeably and usefully. He was all his life fond of visiting other countries, and perhaps a little disposed to underrate his own. Thus he was wont to say, that the thunder-storms of Virginia took away all feelings of awe at those of Scotland, just as the Alps of Switzerland left him nothing to admire in the Scottish mountains. His stay in the new world did not much exceed a year, owing to the breaking up of the family establishment by the death of the father of his young friends. After visiting New York and Philadelphia, he returned to his native place towards the close of the year 1789.

From some letters to his family, written about the time of his leaving America, his thoughts seem to have been anxiously directed to his future means of employment and support; and one of his schemes appears to have been to try his fortune in India, probably as a civil engineer. This notion recurred afterwards, but without leading to any results. His next field of adventure was London, whither he proceeded in January 1790, carrying with him various letters of recommendation; one of which was written by Dr

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1 "The great error," says he, "in modern education consists in the undue attention paid to the dead languages, which consumes the precious time that should be devoted, during the freshness of youth, to the higher intellectual pursuits." (See Preface to his Elements of Geometry, published in 1828.)

2 See vol. ii. p. 193. Adam Smith, then drawing near the close of his career. It was on this occasion, if our recollection does not mislead us, that Dr Smith exhorted his young friend never to approach any author whose favour he might wish to win, without first reading his book, lest the conversation should happen to turn that way. One of Mr Leslie's objects in visiting the capital, was to ascertain what success he might expect from a course of Lectures on Natural Philosophy; and the information he received soon satisfied him, as he says in a letter to one of his brothers, that "rational lectures would not succeed." He therefore employed himself for some time in writing for the Monthly Review, and in executing literary jobs delegated to him by his countryman Dr William Thomson, author of the continuation of Watson's History of Philip the Third, and of many other works now forgotten, and who was much in the habit of lending his versatile pen, as well as his name, to those who required the assistance or recommendation of either. But a more eligible and suitable connection was ere long opened to him, by the invitation of the younger Wedgewoods, who had been his fellow-students at Edinburgh, to reside with them, and superintend their studies. He readily acceded to their proposals; and proceeded, in April 1790, to their residence at Etruria, in Staffordshire, where he remained till the close of 1792, in the enjoyment of a liberal salary, and of society at once agreeable and intelligent. This was, in every sense, a happy and profitable period of his life. The time not devoted to tuition was assiduously employed in experimental investigations, and in completing a translation of Buffon's Natural History of Birds, which he had previously undertaken for a London bookseller. It was published in 1793, after he left Etruria, in nine volumes octavo. Though executed with fidelity and vigour, it was valued by himself, at least after he became otherwise eminent, only as having, by the sum which it procured him, laid the foundation of that pecuniary competency which he early foresaw to be necessary to the independent prosecution of his favourite studies; and which his industrious and prudent habits enabled him in no long time, in a moderate degree, to attain. The preface, however, speaks of this "first attempt" with some anxiety; and endeavours to bespeak favour for it as executed "at an early period of life, and in the retirement of the country." This preface is written in that nervous, but strained and ornate style, which characterises his after writings. His first contribution to Natural Philosophy, entitled Observations on Electrical Theories, was also written at Etruria; and was, in 1791, transmitted to the Royal Society of Edinburgh, for insertion in their Transactions. This was promised; but performance having, as he thought, been long and unhandsomely deferred, he indignantly recalled his Paper, and laid it aside for many years. It did not, indeed, see the light till 1824, when he was induced to publish it in the Edinburgh Philosophical Journal, conducted by his distinguished friend Professor Jameson.

About the period of the close of his agreeable engagement at Etruria, which was occasioned, we believe, by the ill health of Mr Thomas Wedgewood, and the marriage of his younger brother, a Cornish gentleman with whom he had become acquainted at that place proposed to engage him as a companion in an extensive tour through Greece, Egypt, and the Holy Land. Ever fond, as he was, of visiting foreign countries, particularly those hallowed by memorable events or classical associations, the proposal could not but prove agreeable to him, and it was accordingly embraced with alacrity. The tour was to commence early in 1793; but a change of plan having been decided upon without his concurrence, and by which he found that his observations were to be transferred to another, he indignantly relinquished the engagement. His intention to visit these interesting countries, when a fit opportunity should occur, remained with him through life; and, at a period nearly forty years subsequent to this,—in his last years, indeed,—he actually made some preparations for a year's sojourn in Egypt and Palestine, from which he was diverted only by engagements and avocations of which he found it difficult to disencumber himself.

After leaving Etruria, he passed some months in Holland; a country which, like Descartes, he seems to have thought peculiarly suited to secluded study, and where he at this time acquired the German language. Thereafter, he returned to Largo, where he remained for about two years, devoted to experimental researches, in the course of which he invented and perfected his Differential Thermometer; the parent, if we may so speak, of that beautiful family of philosophical Instruments, with which he enriched the Treasury of Science, and amplified and variegated the means of physical inquiry. His ingenuity had been early exercised in some attempts to construct an accurate Hygrometer, and these ultimately suggested to him the well-known contrivance above named—a contrivance happily adapted to the measurement of the smallest variations of temperature, and which richly rewarded his inventive powers by its ministry to the achievement of his subsequent discoveries. It has generally, indeed, been allowed to be one of the most useful as well as elegant inventions that inductive genius ever applied to the investigation of chemical changes. At a later period, when his name had attained a high degree of celebrity, he, like most of the other sons of genius, was made to feel that fame brings with it pains as well as pleasures; for it was now discovered that the Differential Thermometer, instead of being an invention of his own, perfected, as he has himself recorded, in the course of a series of experiments on the evaporation of ice, which the severe winter of 1794–5 afforded him an opportunity of performing, was in reality a plagiarism, if not from Van Helmont, who died in 1644, at any rate, from John Christopher Sturmius, who died some sixty years later. Such was one attempt to impeach the originality of this eminently inventive experimentalist. An Instrument of which all the world remained ignorant, till he, by means of it, told the world the better part of all it yet knows concerning the phenomena of radiated heat, was discovered to have been furtively purloined from one or other of these worthies! Neither the authors nor the abettors of this allegation pretended that either Van Helmont or Sturmius ever dreamt of such applications, or derived such results from their supposed invention, as were reserved, by some caprice of chance, no doubt! for its luckier plagiarist; and it is now, we believe, allowed, that this is just one of those cases of curious but partial anticipation so frequently to be met with in the history of science, and where the ultimate discoverer shows, by his skilful and fruitful employment of the disputed inven-

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1 See vol. xi. p. I. 2 These Instruments, viz. the Differential Thermometer, Hygrometer, Hygroscope, Photometer, Pyroscope, Ethrioscope, and Atmosmeter, are all described, and their principles explained, by himself, in the articles Climate and Meteorology. The latter, like the former, will, at the proper place, be transferred, to this work, from the Supplement to the preceding editions. Properly speaking, the Hygrometer was the parent instrument; the Differential Thermometer having been invented in the course of his endeavours to improve it; but as the Hygrometer, in its latest form, is only a modification of the other, it may be represented as derived from it. See the article Cold. 3 See the article Meteorology. In the spring of 1796, Mr Leslie received an invitation from his friend Mr Thomas Wedgwood, to accompany him in a tour through the north of Germany and Switzerland. To this proposal, which was every way agreeable, he immediately acceded. They arrived at Hamburg about the first of May, and employed that and the next four months in their tour, part of which was performed on foot. He alludes to their observations in the course of their journeys amongst the mountains of Switzerland, in one of the notes to his work on Heat; but of this, as of all his subsequent tours on the Continent, he kept regular Journals, which are still preserved, and which show that he was no less observant of the social, moral, and economical condition of the countries he visited, than of their geological, meteorological, and physical aspects.

For some years after the period just mentioned, he seems to have employed himself in his experimental pursuits, and to have divided his time, chiefly, between London and Largo; to which place, and to the society of his family, he ever was fondly attached. His earnings by literary labour, and his allowances, had raised his humble fortune to what a philosopher might view as an independence; and he accordingly employed or amused himself as his own inclinations dictated. Early in the summer of 1799 he set out with an old college acquaintance on a tour to the northern kingdoms of Europe; in the capitals of which, the latter, who had for some time been settled in Spain as a merchant, had business to transact. After traversing Denmark, part of Norway, and Sweden, they proceeded through Brandenburg to Berlin; and from thence returned to England about the end of November. From his Journal of this tour, which is more detailed than any of those he subsequently kept, the Swedish mines appear to have formed particular objects of his attention. One of his entries records his having, before quitting Hamburg, written an account of his Hygrometer, for insertion in Vogt's Magazine, and in the Annales de Chimie.

In the following year, he published the Paper just mentioned, but with some alterations, in Nicholson's Philosophical Journal. It is entitled a Description of an Hygrometer and Photometer; and was followed with Additional Remarks on these Instruments. In the same year, he also published, in that Journal, a Paper On the Absorbent Powers of the Different Earths; and other two, containing Observations and Experiments on Light and Heat, with Remarks on the Inquiries of Dr Herschel on these objects. These small pieces are very valuable, as showing the progress of his researches and discoveries in that field of inquiry which their titles indicate.

The results of his more extended investigations were long to appear before the world in a different shape. Having collected at Largo all the necessary apparatus, he prosecuted with ardour a series of experiments, which enabled him, in the years 1801 and 1802, to compose the bulk of his celebrated work on Heat. In the latter year, "the gleam of peace," as he tells us in his usual ornate style, "tempted him to indulge in a temporary suspension; and to repair to the famed capital where the treasures of art and science are so profusely displayed. In that vortex of pleasure and centre of information, I spent," he adds, "several months very agreeably; but the work I had undertaken recalled my thoughts, and I hastened again to my retreat."

His Experimental Inquiry into the Nature and Properties of Heat was here at length completed. It was published at Leslie, London in the spring of 1804, with a dedication, couched in terms of strong and affectionate friendship, to Mr Thomas Wedgewood, the companion of his studies at Etruria, and of his first continental tour. The early death of that ingenious and excellent person, whose delicate health is here feelingly alluded to, was always mentioned by him as a public as well as private misfortune. The originality and boldness of the peculiar doctrines of the Inquiry, and the number of new and important facts disclosed by its ingenious experimental combinations, conspired to render it an object of extraordinary interest in the scientific world; and, indeed, it must ever be viewed as constituting an era in the history of that branch of physical science which forms its subject. The Royal Society of London unanimously adjudged to its author the Rumford Medals appropriated as the reward of discoveries in that recollected province. As a philosophical disquisition, it is far, however, from being perfect. Its hypotheses are not warranted by the sober maxims of inductive logic; and its method and style are alike liable to serious criticism. But it would be difficult to name any work in the whole range of physical science more strongly indicative of a vigorous and inventive genius; and it must be allowed by all, that its beautifully devised experiments, and its large stock of new observations, far more than atone for its questionable theories, and for that desultory arrangement, and those ambitious modes of expression, which so often mar its reasonings and obscure its sense. More than ten years before the appearance of this work, Mr Leslie wrote an essay on Heat and Climate, which contains some of the theoretical opinions advanced in the former, as well as the germs of some of its discoveries. It was read at two successive meetings of the Royal Society of London in the spring of 1793; but it was not admitted into the Transactions of that body. Its aspiring author was not of a disposition to be checked in the career of inquiry by this repulse; and he did not shrink from bringing his Paper forth, in 1819, from its long oblivion of twenty-six years; he having then published it, for the first time, in Dr Thomson's Annals of Philosophy.

Twice before that period of his life at which we are now arrived, Mr Leslie had appeared as a candidate for an Academical Chair; first in the University of St Andrews, afterwards in that of Glasgow, and on both occasions without success. He was again to try his fortune in the same line in the Metropolitan University. Early in the year 1805, a vacancy occurred in its Mathematical Chair, owing to the removal of Professor Playfair, on the death of Dr John Robison, to that of Natural Philosophy. This afforded a new opening to his academical ambition; and he was particularly desirous to occupy a Chair upon which the names of the Gregories, of MacLaurin, of Matthew Stewart, and of Playfair, had shed so much lustre. He accordingly presented himself as a candidate; and, with his now high reputation as a discoverer and original thinker, and his known eminence in mathematical science, it was not to be expected that he could have any formidable competition to surmount. Nor did there occur any, in as far as fame or talents were concerned. His principal competitor, though a man of amiable character, and respectable attainments, was wholly unknown in the scientific world, and as inferior to him in abilities as in renown. But he was one of the Ministers of the City, and supported with all the influence of that body; then pretty generally suspected of a wish to secure a monopoly of the

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1 See Nicholson's Journal for 1800, vol. iii., p. 461-518, and vol. iv., p. 196, 344, 416. 2 Preface to the Experimental Inquiry on Heat. 3 See vol. xiv., p. 5-27, and vol. xvi., p. 7, for some just observations by the very able Editor. Philosophical Chairs of the University. It soon, however, became known that the Patrons were determined to decide upon a comparison of claims, and that Mr Leslie must triumph. In this state of things, and in an evil hour for themselves, the City Clergy were induced to raise an objection to his eligibility, on the serious ground of his having, in one of the notes appended to his work on Heat, approved of a doctrine directly leading to atheism. We are sorry to be obliged to notice this discreditable proceeding; but it forms too memorable an occurrence in Mr Leslie's life to allow us to pass it without some animadversion. In the note alluded to, the author, though no metaphysician, and in general rather a contemner of metaphysical science, was, naturally enough, led to illustrate what he had said in the text with reference to the unphilosophical opinion that impulse is necessary to the production of motion, by some remarks on Causation. He prefaced these by observing, that Mr Hume was the first who treated this subject "in a truly philosophical manner;" and that "the unsophisticated notions of mankind are in perfect unison with the deductions of logic, and imply nothing more at bottom, in the relation of cause and effect, than a constant and invariable sequence." Founding upon these remarks, the Ministers of Edinburgh charged him with having "laid a foundation for rejecting all the argument that is derived from the works of God to prove either his Being or Attributes." This heavy charge was preferred in a formal Protest, tendered by them to the Patrons of the University, in which they alleged that, in the election of Professors, the former were, by the charter of erection, bound to act with the advice of the Ministers. That advice was, in the present instance, given with sufficient emphasis; but the Patrons, much to their honour, treated it as it deserved; and Mr Leslie, to the great joy of all liberal minds, was, in March 1805, elected to the Mathematical Chair. The efforts of the disappointed junto did not, however, cease with this rebuff; nor did they desist from their ill-starred opposition, till a decision of the General Assembly of the National Church, pronounced on the 23d of May, after a memorable debate of two days, satisfied them that persecution had now exhausted its resources, and that its hopes must, however sorrowfully, be relinquished. Dismissing any supposition of interested designs, and even allowing that Mr Leslie's expressed opinion as to Causation, if taken apart from the subject-matter of his book, or left unexplained, was calculated to occasion some alarm in the minds of the pious, still, impartial history ever must brand the proceedings of his opponents as alike uncharitable, unfair, and arrogant; and as deeply injurious to the character of that Church with whose name and authority they clothed themselves. It was on all hands admitted, that if Mr Leslie had, by a single word, limited his observations to Physical causes, they would have been wholly free from objection; and, surely, it required a most perverse and intolerant construction to extend to any but such causes, the observations of an illustrative note to a work purely physical, and undeniably levelled at those theories which resort to certain invisible intermedia, in order to account for the connection of physical sequences. But this was not all. Mr Leslie, on being informed of the charge, immediately declared, in a very pointed Letter laid before the junto, that his observations "referred entirely to the relation between cause and effect, considered as an object of physical examination." Yet was this prompt explanation disingenuously disregarded—nay suppressed; whilst his persecutors—owing to an ignorant blunder in their statement of what they conceived to be the true notion of Causation—were themselves obliged to have recourse to explanation, in order to show that their doctrine was not identical with that of the Fatalists and Spinoza.

Mr Leslie commenced and prosecuted his official duties with great ardour. He entertained lofty ideas of the dignity and utility of the professorial character, and was thus disposed to make all the exertions necessary to success. Though the bent of his genius lay more to Physics than to Pure Mathematics, he had cultivated the study of Geometry with kindred relish; and with an admiration, in particular, of the analytical investigations of the ancient geometers, which led to his happiest essay in that science. As a teacher, he not only laboured to promote the study, but to procure for it a larger share of attention than our academical system usually assigns to it. His instructions were better suited, perhaps, to youths of superior ability than to ordinary students; but reputation and intellectual power produced their usual results, and secured for him an attendance as numerous as could be expected by any teacher, during the whole of the fifteen years that he occupied the Mathematical Chair. Soon after his election, he resolved to compose and to publish, at successive intervals, a complete "Course of Mathematics," digested and arranged according to his own ideas of what was wanted towards promoting a purer taste in the cultivation of the science. Of this Course, the first volume, comprising Elements of Geometry, Geometrical Analysis, and Plane Trigonometry, was published in 1809; and it has gone through several very extensive editions. The first part of it has been viewed as the least perfect and useful; but his own favourite portion, on Geometrical Analysis, has been extolled by the most unsparing critics of the former, as "a great acquisition to Elementary Geometry;" and as calculated to keep alive the knowledge of a most beautiful and interesting branch of the mathematics, which has been too much overlooked during the improvement of the more general and powerful methods of algebraic investigation. Abroad, it seems to have been viewed in a light equally favourable; as it was speedily translated into the French and German languages. He re-produced it, with considerable emendations, in the second volume of his "Mathematical Course," which, besides, contains the Geometry of Curves Lines. This volume was not published till 1821—an interval of twelve years having thus elapsed from the appearance of the first. A third volume, on Descriptive Geometry, and the Theory of Solids, was still wanting to complete his original design; but his removal to another Chair, and other circumstances, called his attention to different objects, and his "Mathematical Course" was thus left unfinished.

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1 Inquiry into the Nature of Heat, p. 133, and Note 16, p. 522. 2 Professor Stewart's Short Statement of Facts relative to the Election of a Mathematical Professor in the University of Edinburgh, p. 44. 3 See Report of the Debate, published at Edinburgh, in October 1805. 4 See Professor Stewart's Short Statement, p. 36, and Report of the Debate in the General Assembly, p. 16. 5 See Short Statement, p. 77–94, and Report of the Debate, passim. This remarkable controversy gave rise to a number of other publications; but none of them, with the exception of these two, an admirable Letter to the author of a Reply to the former, by Professor Playfair, and Dr Brown's Observations on the nature and tendency of the doctrine of Mr Hume concerning cause and effect, with other two pieces by that most acute metaphysician, have the least chance of interesting posterity. The two pieces alluded to were, A short criticism of the terms of the charge against Mr Leslie in the Statement of the Ministers of Edinburgh, and An examination of some remarks in Dr Inglis's Reply to Professor Playfair. The Reply by Dr Inglis was the ablest production on the clerical side, and certainly evinced a good deal of controversial ability.

Edinburgh Review, vol. xx, p. 98. He was induced, at a late period of his life, to recast the first volume in a greatly abridged form. His object in doing so was to accommodate it to the use of those who, in riper years, become desirous to supply the defects of early education, and to qualify themselves for obtaining some knowledge of Natural Philosophy. This abridgment appeared in 1823, under the title of *Rudiments of Plane Geometry, including Geometrical Analysis, and Plane Trigonometry*. In connection with his mathematical works, though forming no part of his "Course," we may here mention the profound and learned treatise on the *Philosophy of Arithmetic*, which he published in 1817. It was a republication, with considerable alterations and additions, of one of the numerous articles contributed by him to the *Supplement* to the former editions of this Encyclopedia.

It was not to be expected that the labours of the Mathematical Chair would wean Professor Leslie from his experimental inquiries. His fine Instruments were always at hand, and always in use, in connection with some ingenious conception or other. Early in the summer of 1810, he determined to proceed with some experiments previously suggested in the course of his researches with his Hygrometer, but which had for some time been suspended; and they now conducted him to the discovery of that beautiful process of Artificial Congelation, by which he was enabled to produce ice, and even to freeze mercury, at pleasure. The discovery was achieved by means of a happily-conceived combination of the powers of rarefaction and absorption, effected by placing a very strong absorbent under the receiver of an air-pump. It was in the month of June of that season that the discovery was consummated! We happened to witness this consummation,—at least the performance of the first successful repetition of his process,—and we never shall forget the joy and elation which beamed on the face of the discoverer, as, with his characteristic good nature, he patiently explained its principles, and the steps by which he had been led to it. We could not but feel, on looking at, and listening to him, how noble and elevating must be the satisfaction derived from thus acquiring a mastery over the powers of Nature, and enabling man, weak and finite as he is, to reproduce her wondrous works! Proportioned to the admiration which such achievements are calculated to excite, ought to be the disapprobation of any unfair endeavours to lower or depreciate them. We have already alluded to an attempt to divest this illustrious experimentalist of the honours connected with his Differential Thermometer; and we have now to add, that several years after the discovery of his process of Artificial Congelation, there were some similar endeavours to transfer the merit of it to a gentleman of the name of Nairne. The claim for him was founded on a Paper published in 1777, in the *Transactions* of the Royal Society of London; from which it appeared that he was acquainted with the facts, that evaporation produces cold, and that sulphuric acid, the absorbent employed by Mr Leslie, imbibes moisture. But in order to decorate Mr Nairne with the laurels of the latter, his depreciators ought to have been able to show, that the former had combined the properties alluded to, in a manageable process for the production of ice *ad libitum*. In such an attempt they must have failed ignominiously; and, perhaps, there is not in the whole history of science any more triumphant reply to a charge of plagiarism, than is furnished by the admitted facts, that with Mr Nairne's Paper before them for a long course of years, the scientific world remained utterly ignorant of the existence of any such process till the date of Mr Leslie's discovery; nay, that with his description of that process in their hands, the most distinguished experimentalists of the capital failed in their trials of it, till it was performed there by himself, in the ensuing summer!

In a letter from London to one of his friends, written in June 1811, he says, "My package has at last arrived, and I shall proceed without delay to make my debut." It was only now that the experiment was first successfully performed in the capital. This took place before a meeting of some members of the Royal Society, and others. The discovery was announced in the same year, in the Memoirs of the French Institute; and the process itself was afterwards exhibited, in presence of that body, by M. Pictet and M. Gay-Lussac. He did not himself publish any detailed account of his experiments and views on this interesting subject till 1813, when he explained them at considerable length, in a small volume entitled *A short Account of Experiments and Instruments depending on the Relations of Air to Heat and Moisture*. This publication, which was partly intended to promote the circulation of his Instruments, and to explain their principles, would have been infinitely more useful had its author superadded the powers of methodical and elementary exposition to his other endowments. But notwithstanding its defects in these particulars, it was much commended by those competent to appreciate its value as a contribution to science. Closely connected with the subjects of this treatise, and which, therefore, we may notice here, though it did not appear till some years later, was an ingenious Paper, published in 1818, in the *Transac-

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1 See the article Col. D. The successive steps of the discovery are here recorded by himself, in those verba arcania which the bent of his genius so strongly prompted him to employ.

2 Some very complete and curious legal evidence of these facts was adduced by Professor Leslie, in 1822, in a prosecution which he was advised to institute against the publisher of a well-known Magazine, for a series of libels inserted in that work, and in one of which he was accused of having stolen the discovery alluded to, from Mr Nairne. Amongst other witnesses, two very distinguished Chemists were examined on that occasion—the late Dr Marcey, and Dr Thomson, Professor of Chemistry in the University of Glasgow. We shall extract a small portion of that of Dr Marcey, to whom Mr Leslie was, personally, but little known.—Q. Is it your opinion that Mr Leslie is to be considered as having borrowed or stolen this discovery, or do you consider his discovery to be original?—A. Some of the facts were known long before, but the process itself is perfectly original.—Q. Is the discovery of Mr Leslie analogous to other discoveries in the science of chemistry?—A. There is hardly any discovery of the least value that has been made in that science but from the known properties of bodies. It is by combining those properties, so as to produce certain effects, that a discovery is made.—Q. Then, you mean to say that Mr Leslie has done what none before him ever accomplished?—A. Certainly. He has done what the whole philosophic world, with all the facts before them for a long period, had not been able to accomplish.—Q. When and by whom was the experiment first successfully performed in London?—A. It was successfully performed in London by Mr Leslie himself. My belief is, that no one succeeded in this experiment, in London, until Mr Leslie himself showed the way.—Q. Do you know that Sir Humphry Davy tried and failed?—A. I cannot positively say; I believe he tried it, but without success." (Report of the Trial by Jury, Professor Leslie against William Blackwood, p. 82-6.)

3 See Mémoires de la Classe des Sciences Mathématiques et Physiques, t. xii. p. 89; t. xiv. p. 117-18.

4 See Edinburgh Review, vol. xxiv. p. 339-52, and Dr Thomson's *Annals of Philosophy*, vol. ii. p. 457-62, for a skilful analysis of this treatise. In the Trial above alluded to, the party prosecuted took an issue to show that the article in the Edinburgh Review in commendation of the work, was written by Mr Leslie himself. The attempt was not made; and it is hardly worth while to mention, with reference to such a charge, that the article was written by a very able chemist, the late Dr John Murray. Leslie, Sir John.

On certain impressions of cold transmitted from the higher atmosphere; with a description of an Instrument adopted to measure them. The Æthroscope, the instrument here alluded to, is, in another place, described, in the poetical language of its author, as "fitted to extend its sensation through indefinite space, and to reveal the condition of the remotest atmosphere."

In the autumn of 1814, Professor Leslie indulged himself with a tour of six weeks in France and the Netherlands. He never was satisfied if he allowed a vacation to pass without seeing or revisiting some foreign scenes. One or two extracts from Letters written by him on the present occasion, may be here introduced, as either curious in themselves, or characteristic of the writer. Writing from Paris, on the 1st of August, he says, "you know that it was not my intention at present to mix much with the Scavans. But I have been so well received, and even feasted by them, that I may perhaps depart a little from my original design. Humboldt has been very kind and attentive to me, and introduces me wherever I want. They are much better acquainted with what we are doing than I should have imagined. My book on Heat is better known than in England. I was even reminded of some passages in it which in England were considered as fanciful, but which the recent discoveries on the Polarity of Light have confirmed. Even Laplace has, in consequence of some observations of mine, silently omitted a passage in the last edition of his Système du Monde. I paid a visit the other day at Arcueil. Berthollet has a fine chateau seated on a bank amidst gardens, vineyards, &c.; and Laplace has another, little inferior, and adjoining to the grounds. I dine with Laplace next Sunday. Some person had informed him that I was the author of a critique in the Edinburgh Review on a paper of his, and he had sent an answer to me, which, however, I never received." The following extract from another letter, written at Bordeaux, in the beginning of September, gives a rapid and lively sketch of his journey to that place:—"My tour has furnished what I wanted—a number of images of the milder and hotter regions of the Continent. From Paris I proceeded to Macon, over a rich and well-cultivated country, covered with wheat and vineyards, the crop for the most part already gathered in. Thence I descended the Somme, a fine, clear river, to Lyons; the banks covered with luxuriant vineyards stretching to a range of hills, and the waved surface sprinkled with trees, intermixed with frequent villages, and lively villas, all of white limestone. At Lyons I met with the celebrated Baron Zach, and was conducted by him in his carriage to the fountain of Vaucluse, Avignon, and thence to Marseilles. His society was particularly entertaining and instructive. We now passed through the country of the mulberry, the fig, and the olive; but I confess that Provence did not come up to my expectation. I have seen, what I had longed to see, the awful fountain of Vaucluse, and the blue expanse of the Mediterranean; but the shores at Marseilles are terminated by gray, naked rocks, shooting fantastically to great heights. I staid some days at Marseilles, and spent most of my time at a country house occupied by the old Duchess of Saxe-Gotha, with whom Baron Zach lives in quality of Cham-

berlain. I found her very kind and affable, and extremely glad to hear any news of the Royal Family of England. From Marseilles I returned to Avignon, and then crossing the Rhine, proceeded to Nismes, over a country extremely fertile and interesting. This is almost a Roman town. There is a temple to Augustus, beautifully Corinthian, a fine temple of Diana, and an amphitheatre almost entire, capable of holding twenty thousand spectators. I now proceeded to Montpellier, and saw the majestic range of the Pyrenees stretching on our left, and covered with eternal snow. Montpellier is an interesting place,—its Botanic Garden rich, and its promenades superb. I then proceeded to Toulouse. In leaving it, the carriage plunged into a hollow across the road; it was eleven at night, but the moon shone full, and lighted up a fine rich plain. I shuddered when told that we had just crossed five hundred dead bodies, which had been thrust into a cut or trench of the road, after the late battle. The road to Bordeaux runs near the course of the Garonne, through one of the finest and richest countries I have ever seen." From this place he returned to Paris, and, after a short stay, proceeded through the Netherlands to Rotterdam, where he took shipping for Scotland.

The publication of the Supplement to the three editions of this Encyclopaedia immediately preceding the present one, commenced towards the close of 1815, and was continued progressively till its completion early in 1824. To that work, which was undertaken upon an unusually extensive plan, and which aimed at procuring the highest attainable assistance, Mr Leslie was throughout a Contributor. His contributions, surprisingly numerous when his other avocations are considered, display all the powers and attainments for which he was remarkable. Nor was it by his writings alone that he aided this publication. His advice, his invaluable information,—amazing alike for its minuteness and extent,—and his influence, were always at the service of its Editor, whose acknowledgment of these various obligations has long been before the public. But it is due to Mr Leslie's memory to specify in this sketch of his life what the work owes to his genius and knowledge. Ranged in alphabetical order, his writings in it occur under the following heads: Achromatic Glasses; Acoustics; Aeronautics; Andes; Angle; Angle, trisection of; Arithmetic, palpable and figurate; Atmosphere; Barometer; Barometrical Measurements; Climate; Cold and Congelation; Dew; Interpolation; Meteorology.

Another work which at intervals enjoyed the benefit of his co-operation, was the Edinburgh Review. But his contributions, though commencing in the year 1809, were not numerous. They helped, however, and that in an eminent degree, to strengthen and diversify the scientific department of that Journal; whilst those regarding Voyages and Travels combine scientific observation with powers of writing of no ordinary description. Among his principal articles may be mentioned those on the Physical and Chemical Memoirs of the Society of Arcueil; on the history of the Barometer; on Delambre's work on the Arithmetic of the Greeks; on Von Buch's Travels; on Humboldt's Physical View of the Equatorial Regions, and on his Travels; and on the attempts to discover a North-West Passage to Asia. The picture in the last, of the revolu-

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1 This must allude to a Paper by Laplace On the Motion of Light in Diaphanous Media, in the Mémoires de la Société d'Arcueil. These Memoirs were reviewed by Professor Leslie, in two articles, in the fifteenth volume of the Edinburgh Review, published in 1816. They formed his first contributions to that Journal.

2 See Preface to Supplement, p. 13.

3 The present edition is enriched with the whole of these articles. That part of the article Arithmetic, which relates to palpable notation, has been omitted, with the exception of the curious disquisition on the Absent, which is printed separately in this edition. The article Interpolation is, in it, annexed to that on Logarithms. In the year 1819, a new field of professorial labour was opened to Mr Leslie, by the vacancy in the Chair of Natural Philosophy, occasioned by the death of one of the greatest ornaments of the University, Mr Playfair. Mr Leslie was on his return from one of his summer trips to the Continent when this lamented occurrence took place. The news met him on being put ashore at Largo, and is thus mentioned in a letter from that place, written on the first of August; in which he also describes an accident that had nearly, as he says, deprived the University of another Professor: "After having been detained for about a week in Holland, and after a tedious but agreeable passage of near ten days, I was at last put ashore here, from a sloop bound from Rotterdam to Grangemouth. Everything looked joyous; but I had soon the tidings of poor Playfair's death, which was most unexpected and distressing. The loss to the university is severe. . . . . I suspect that you were nearly deprived of two professors at once; for on Tuesday the 13th ultimo, I met with an alarming accident in Holland. I had passed the evening at a clergyman's with an intelligent merchant, late Provost of Aberdeen. On coming out of the house, at the end of the Boontiges Street, or the street with rows of trees, the Maas running close, I stepped hastily forward to show him the Comet, and the quay being quite dark, I fell eight feet, and then plunged four feet in the water. This was the affair of an instant, and I felt that I was drowning; but I quickly recovered myself; and was helped out, with no damage but that of a bruise sustained in the fall." The eyes of the Patrons, and others interested in the University, were now turned to Mr Leslie, as the person best qualified to fill the vacant Chair. Two years before, when Mr Playfair was abroad, and an arrangement failed for carrying on the Class, Mr Leslie, at the very commencement of the session, unhesitatingly undertook the task for his absent colleague; but, independently of this circumstance, his eminence in mathematical and physical science was such, that no one else could reasonably be thought of; and he accordingly was, without difficulty, appointed to the Chair; being thus a second time, but in more melancholy circumstances than on the former occasion, nominated a successor to his early friend.

The Chair to which he was thus unexpectedly called was unquestionably that for which he was best suited; and had he happened to be placed in it at the commencement of his professorial career, science in all probability would have derived greater benefits than she actually reaped from his powers. The time spent in his mathematical compositions would have been more profitably employed in that wider and richer province which he was so peculiarly qualified to cultivate. One of the first cares of his new situation was the extension of the Apparatus required for that greatly enlarged series of experiments which he thought necessary for the illustration of the Course. This, indeed, was an object of which, from the first to the last year of his incumbency, he never lost sight; and it is due to him to state, that it was through his exertions that the means of experimental illustration, in the Natural Philosophy Class, were for the first time made worthy of the place. Viewing him merely as a teacher, it must be admitted that he was not eminent. He was apt to forget, or rather did not perceive, that the connecting links between premises and conclusion, though familiar to the teacher, may, to Sir John Leslie, be all unknown; that views quickly reached by the acquired perceptions of the one, must be opened up, step by step, to the yet imperfect vision of the other; and that it is the imperative duty of a public instructor to bring down knowledge from its highest spheres, and place it on a level adapted to the powers of unpractised understandings. His views of the nature of science were grand and animating; and his strictures on the great discoveries which constitute the epochs of its history, sometimes swelled into lofty strains of admiration; but, generally, in lecturing, as in writing, he wanted that consecution of thought, and that perspicuity of exposition, without which reasoning cannot be made intelligible, nor its conclusions satisfactory. Still, the extraction of his numerous experiments, the celebrity of his name, and the opinion entertained of his extraordinary powers, joined with great simplicity and affability of manner, concurred to secure him the respectful homage of his students, and to sustain the glory of the University. In 1823, he published, chiefly for the use of his class, a volume entitled Elements of Natural Philosophy; being the first of a Course intended to extend to three, and to exhibit a comprehensive view of the principles of that congeries of sciences which we are accustomed to class under the above term. Here, as was the case with his Mathematical Course, his plan was not completed; for he published no part of it but the volume mentioned, which includes only Mechanics and Hydrostatics. A second edition of this volume, corrected, and augmented with Notes, was published in 1829, three years before his death.

Mr Leslie had early determined to visit Italy at a fit opportunity; and he at last, in the summer of 1823, carried his design into execution. He set out with a mind still glowing with youthful enthusiasm, at the prospect of beholding the "eternal city;" but, whether from his entertaining too lofty conceptions, or from his view being too hurried and superficial, the tour, in as far at least as respected that crowning object of it, ended in disappointment. The following letter, written at Innsbruck on the 11th of August, contains a brief outline of his journey. "I have thus reached the frontiers of Germany on my return from Italy. I have fortunately achieved the principal objects of my tour; and though I have travelled slowly, I have seen a great deal in a short time. From Geneva I proceeded by Lausanne up the Valois to Brieg—thence crossed the Simplon, and descended through the plains of Lombardy to Milan. From this place I advanced by Parma and Modena to Bologna—next crossed the Appenines to Florence—again crossed another part of that broad chain to Rome. For various reasons, I made the 'eternal city' the limit of my journey. I therefore traversed the Appenines again to Ancona—skirted a considerable portion of the Adriatic—returned to Bologna, and thence proceeded to Mantua. I spent two days, about twenty miles from that place, at an old chateau, the residence of Acerbi, who accompanied me to Verona. Thence I went to Trent, and journeying through the Tyrol, have reached this spacious, interesting city. Italy has rather fallen below my expectations, whilst Switzerland has surpassed my early impressions. The passage of the Simplon alone is worth the journey; but the route through the Tyrol, though not so sublime, is highly picturesque. Italy has every thing on a grand scale."

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1 Mr Playfair expressed his gratitude, in very warm terms, for the promptness with which Mr Leslie, on this occasion, relieved him from what would have otherwise proved an unpleasant predicament; and it is but justice to the latter to mention the act, as showing that the placability of his nature, aided perhaps by the consciousness of intellectual power, had entirely obliterated those feelings which the somewhat severe critique of his Geometry in the Edinburgh Review, known to have been written by Mr Playfair, would have left to rankle, and produce the ordinary results, in a mind more irritable or less magnanimous. scale. The plains, mountains, rivers, works of art, are all majestic and noble. But there is no comfort. Rome itself stands in the midst of a desert. Its grandeur has always been artificial—the result of force or fraud. I have seen whatever is most interesting; and I am inclined to differ very widely from our ordinary travellers. I heard much of the malaria, but I escaped untouched. I suffered little from the heat, and bore it better than the natives. Conformably to the custom, however, I was a sort of prisoner during a great part of the day—the windows shut to exclude every ray of light; and I was only called at times to look out, by the babbling chant of the Monks, with their torches and crosses, carrying the dead to their graves, and followed by the Charitable Brethren, like ghosts, apparelled in white sheets, with only holes for their eyes. They seemed better fitted to terrify the living than to comfort the dying." Two years after this, he made another tour on the Continent, in which he seems only to have gone over ground in France, the Netherlands, and Holland, which for the most part he had traversed before. This, we believe, was the last of his journeys abroad.

The only important production of Mr Leslie's latter years was that which formed his crowning benefaction to this work—his Discourse on the Progress of Mathematical and Physical Science during the eighteenth century; which, with others of a similar description, constitute its first volume. The opening tribute to Mr Playfair, of whose history of the earlier progress of these sciences, this Discourse is a continuation, does honour alike to the writer's candour and taste. "The progress of mathematical and physical science during the brilliant period which closed with Newton and Leibnitz, has," he says, "been traced with fidelity and sustained interest by the hand of a master, whose calm judgment weighed impartially the different claims of discovery, whose powers of illustration could expand the fine results, and whose luminous eloquence was commensurate with the dignity of the subject." Nor is his observation on his own task less just; namely, that the more crowded field of discovery which it presents rendered it one of increased difficulty—"its multifarious materials often lying scattered among the countless volumes of the Transactions of learned Societies." His arrangement of these materials, and his view of the whole subject, is comprehensive, vigorous, and spirited; and the greater ease and perspicuity of its style make this the most agreeable of all his writings.

The volumes of the Edinburgh Philosophical Journal, published between 1824 and 1829, contain some small contributions, which may be here mentioned as also belonging to his latter years. The first consists of Remarks on the Light of the Moon and of the Planets; the second, of an Enumeration of the Instruments requisite for Meteorological observations; the third, of a Letter on the Conionometer; and the last, of Observations on the Theory of Compression, applied to discover the internal constitution of our Earth. The characteristic boldness and poetical dress of his speculations are abundantly displayed even in these small productions. In the first of them, he endeavours to show that the moon is a phosphorescent substance, like the Bolognian stone; and he anticipates a period when "she will no longer cheer our nights by her soft and silvery beams; when she will become dim and wane, and seem almost blotted from the blue vault of heaven. To our most distant posterity," he adds, "this prospect is indeed gloomy; but other changes will arise to renovate and embellish the spectacle of the universe." In the last, he carries his reasonings to the startling conclusion, that the crust of the planet on which we tread includes "an immense concavity, not dark and dreary, as poets have fabled, but containing light in its most concentrated state, shining with intense fulgurance and overpowering splendour!"

Early in the year 1832, which unhappily proved to be that of his death, he was, on the recommendation, we believe, of Lord Brougham, then Lord High Chancellor, created a Knight of the Guelphic Order. This honour was also conferred on several other distinguished men of science, at the same time. In a letter mentioning this occurrence, he says, "my holiday title is now of course Sir John; but I shall always retain an affection for my old distinction of Professor." He had but few other titular distinctions of any sort; for he was far from setting any value on those arising from fellowship with Scientific Bodies. He was a member of the Royal Society of Edinburgh, but not of that of London. The only distinction of this kind that he in the least degree prized was his being elected a Corresponding Member of the Royal Institute of France. This took place, with honour, in 1820; the choice, if we recollect rightly, having fallen upon him, in preference to others then proposed, by a majority of thirty-three out of thirty-seven votes.

For a few years before the fatal one above mentioned, his occupations had been agreeably diversified, by his attention to the improvement of a small estate, called Coates, situate near his native place, of which he made a purchase. Here, the house and garden being every way commodious and suitable, and surrounded with scenes endeared by his earliest recollections, he loved to reside; and even those of his friends who most regretted that, his precious time should be wasted on rural occupations, could not but sympathise with his feelings, and rejoice that the honourable labours of the Philosopher had enabled him to secure such a retreat. No one could enjoy more vigorous or constant health; and though of a corpulent habit of body, he was exceedingly active, and fond of exercise. His strength, and the longevity of his family—a circumstance on which he himself founded flattering hopes—alike gave promise of longer life; and it is melancholy to think that its close was but too probably hastened by one of his foibles—a contempt for medicine, and an unwillingness to think that he could be seriously ill. In the last days of October, whilst engaged in superintending some improvements on his grounds, he exposed himself to wet, and caught a severe cold. This was followed by erysipelas in one of his legs, which he neglected, and again imprudently exposed himself in the fields. He soon afterwards became dangerously ill, and expired at Coates, on the evening of Saturday the third of November 1832, in the sixty-seventh year of his age.

It has been well observed by Dr Johnson, that "of every great and eminent character, part breaks forth into public view, and part lies hid in domestic privacy. Those qualities which have been exerted in any known and lasting performances, may, at any distance of time, be traced and estimated; but those peculiarities which discriminate every man from all others, if they are not recorded by those whom personal knowledge enabled to observe them, are irrecoverably lost." To prevent "this mutilation of character," as the same writer calls it, we shall close our narrative with a few details more particularly illustrative of the mind, opinions, and dispositions of this remarkable person. His discoveries, and the facts and controversies connected with them, may be discussed by many; and the full detail of them would require

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1 Johnson's Life of Sir Thomas Browne. more space than can here be afforded; but, having enjoyed all the advantages for observation which long and intimate "personal knowledge" alone can supply, we think it right to endeavour, though briefly, to prevent some characteristic features from being "irrecoverably lost." The portrait may be imperfect; we cannot, indeed, complete it to our own satisfaction on our narrow canvass; but, in as far as the sketch extends, we can honestly say that it is faithfully copied from nature.

It would be impossible, we think, for any intelligent and well-constituted mind, thoroughly acquainted with the powers and attainments of Sir John Leslie, to view them without a strong feeling of admiration for his vigorous and inventive genius, and of respect for that extensive and varied knowledge, which his active curiosity, his excursive reading, and his happy memory, had enabled him to amass and digest. Some few of his contemporaries in the same walks of science may have excelled him in profundity of understanding, in philosophical caution, and in logical accuracy; but we doubt if any surpassed him, whilst he must be allowed to have surpassed most, in that creative faculty—one of the highest and rarest of nature's gifts—which leads to and is necessary for discovery, though not all-sufficient of itself for the formation of safe conclusions; or in that subtlety and reach of discernment which seizes the finest and least obvious qualities and relations of things—which elicits the hidden secrets of nature, and ministers to new and unexpected combinations of her powers. "Discoveries in science," says he, in one of his works, "are sometimes invidiously referred to mere fortuitous incidents. But the mixture of chance in this pursuit should not detract from the real merit of the invention. Such occurrences would pass unheeded by the bulk of men; and it is the eye of genius alone that can seize every casual glimpse, and discern the chain of consequences." With genius of this sort he was richly gifted. Results overlooked by others were by him perceived with a quickness approaching to intuition. To use a poetical expression of his own, they seemed "to blaze on his fancy." He possessed the inventive in a far higher degree of perfection than the judging and reasoning powers; and it thus sometimes happened, that his views and opinions were not only at variance with those of the majority of the learned, but inconsistent with one another. Notwithstanding the contrary testimony, explicitly recorded, of the founders of the English Experimental School, he denied all merit and influence to the labours of the immortal delineator of the Inductive Logic. He freely derided the supposed utility of Metaphysical Science, without perceiving that his own observations on Causation virtually contained the important admission, that physical is indebted to mental philosophy for the correct indication of its legitimate ends and boundaries. His writings are replete with bold and imaginative suppositions; yet he laments the "ascendancy which the passion for hypotheses has obtained in the world." His credulity in matters of ordinary life was, to say the least of it, as conspicuous as his tendency to scepticism in science. It has been profoundly remarked by Mr Dugald Stewart, that "though the mathematician may be prevented, in his own pursuits, from going far astray, by the absurdities to which his errors lead him, he is seldom apt to be revolted by absurd conclusions in other matters." "Thus, even in physics," he adds, "mathematicians have been led to acquiesce in conclusions which appear ludicrous to men of different habits." Something of this sort was observable in the mind of this distinguished mathematician. He was apt, too, to indulge in unwarrantable applications of mathematical reasoning to subjects altogether foreign to the science; as when he finds an analogy between circulating decimals and the lengthened cycles of the seasons! But when the worst has been said, it must be allowed that genius has struck its captivating impress over all his works. Whether his bold speculations lead him to figure the earth as enclosing a stupendous concavity filled with light of overpowering splendour; or to predict the moon's arrival at an age when her "silvery beams" will become extinct; or to ascribe the phenomena of radiated heat to aerial pulsations; we at least perceive the workings of a decidedly original mind. This, however, is not all. His theoretical notions may be thrown aside or condemned; but his exquisite instruments, and his experimental combinations, will ever attest the utility no less than the originality of his labours, and continue to act as helps to farther discovery. We have already alluded to the extent and excursiveness of his reading. It is rare, indeed, to find a man of so much invention, and who himself valued the inventive above all the other powers, possessing so vast a store of information. Nor was it in the field of science alone that its amplitude was conspicuous. It was so in regard to every subject that books have touched upon. In Scottish history, in particular, his knowledge was alike extensive and accurate; and he had, in acquiring it, gone deep into sources of information—such as parish records, family papers, and criminal trials—which ordinary scholars never think of exploring. The ingenious mathematician, the original thinker, the rich depository of every known fact in the progress of science, would have appeared to any one ignorant of his name and character, and who happened to hear him talk on this subject, as a plodding antiquary; or, at best, as a curious and indefatigable reader of history, whom nature had blessed with at least one strong faculty, that of memory. His conversation showed none of that straining after "thoughts that breathe, and words that burn," so conspicuous in his writings. In point of expression, it was simple, unaffected, and correct. Though he did not shine in mixed society, and was latterly unfitted, by a considerable degree of deafness, for enjoying it, his conversation, when seated with one or two, was highly entertaining. It had no wit, little repartee, and no fine turns of any kind; but it had a strongly original and racy cast, and was replete with striking remarks and curious information.

Viewing the whole of his character, moral and intellectual, it must be confessed that it presented some blemishes and defects. He had prejudices, of which it would have been better to be rid; he was not over charitable in his views of human virtue; he was not so ready, on all occasions, to do justice to kindred merit as was to be expected in so ardent a worshipper of genius; and his care of his fortune went much beyond what is seemly in a philosopher. But his faults were far more than compensated by his many good qualities;—by his constant equanimity, his cheerfulness, his simplicity of character almost infantile, his straightforwardness, his perfect freedom from affectation, and, above all, his unconquerable good nature. He was, indeed, one of the most placable of human beings; and, notwithstanding his general attention to his own interest, it is yet undeniable, that he was a warm and good friend, and a relation on whose affectionate assistance a firm reliance ever could be placed. He was fond of society, and greatly preferred and prized that of the intelligent and refined; but no man ever was more easily pleased; no fastidiousness ever interfered with his enjoyment of the passing hour; he could be happy, and never failed to converse in

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1 The substance of some of the following observations appeared in the Newspapers immediately after the death of Sir John Leslie. They may, without impropriety, be used here, by the pen from which they originally proceeded.

2 See Introduction to Elements of Natural Philosophy. his usual way, though in the humblest company; and we have often known him pass an afternoon with mere boys, discoursing to them pleasantly upon all topics that presented themselves, just as if they had been his equals in age and attainments. He was thus greatly liked by many who knew nothing of his learning or science, except that he was famous for both.

He was never married. As to his person,—he was somewhat under the middle size, and corpulent, but strong and well limbed; and though his face was large and florid, there was that about his eyes and forehead which seemed to show that he was no ordinary man. There is a Bust of him by Joseph; a Portrait of the ordinary size, taken a few years before his death, by Wilkie; and a Head, drawn at an earlier period, by Henning, which presents a striking likeness.