for which he obtained a sum that laid the foundation of his pecuniary independence. He soon after proceeded to the United States, in the quality of tutor to one of the family of the Kandolphs; and, after his return, made a tour to the continent, in company with Mr. Thomas Wedgewood. We are not informed at what precise period Mr. Leslie struck out his discoveries respecting radiant heat, and the connexion between light and heat; but his differential thermometer must have been invented some time previous to 1800, in which year it was described in Nicholson's Journal. The results of the inquiries, in which he was so much aided by this instrument, which has been justly pronounced one of the most beautiful and delicate that indicative genius ever contrived as a help to experimental inquiry, were published in his celebrated Essay on the Nature and Propagation of Heat. This appeared in 1804, and was rewarded, in 1805, by the Rumford medal. In the same year, he was appointed mathematical professor in the University of Edinburgh; but had some difficulty in retaining the chair, in consequence of the strenuous opposition of the strict presbyterian clergy, on the ground of his supposed scepticism. In 1809, he published his Elements of Geometry, Geometrical Analysis, and Plane Trigonometry; and, in the following year, he arrived, through the assistance of his hygrometer, (another of his own contrivances,) at the discovery of a process which enabled him to convert water and mercury into ice. In 1813, he published An Account of Experiments and Instruments depending on the relations of Air to Heat and Moisture. In 1819, he succeeded Professor Playfair, in the chair of natural philosophy, a situation for which he was eminently qualified. He made such an improvement in the apparatus belonging to this class, that the number of instruments was, on the whole, increased tenfold, some of the most delicate and beautiful being constructed by his own hands. Of all his great and varied gifts, says one of his biographers, none was more remarkable than the delicacy and success with which he performed the most difficult experiments, excepting, perhaps, his intuitive

sagacity in instantly detecting the cause of accidental failures. Besides the works before-mentioned, he wrote some very valuable treatises on different branches of physics, in the supplement to The Encyclopædia Britannica, and some admirable articles in The Edinburgh Review. Mr. Leslie is distinguished for his inventive genius and vigorous powers, a most retentive memory, and a stock of knowledge which his various reading and active curiosity have rendered very extensive. In that creative faculty, which leads to discovery, few scientific men have excelled him; but in profundity of understanding, in philosophical caution, and in logical accuracy, he has many superiors. Yet however transient may be his fame as a speculative philosopher, his exquisite instruments, and his original and beautiful experimental combinations, have secured to him lasting reputation.

MARCET, (ALEXANDER,) was born at Geneva, in the year 1770. At an early age, he shewed a great inclination to studious pursuits; but, on the death of his father, who entreated him to adopt a mercantile life, he, for some time, turned his attention to commerce, which, however, he soon relinquished, and applied himself to the study of the law. On the breaking out of the French revolution, he was thrown into prison, and with much difficulty saved his life, by submitting to banish himself for the space of five years. Accordingly, in 1794, he repaired to Edinburgh, where he became a medical student; and, in the latter part of 1797, took his degree of M.D. Shortly after, he commenced practising, as a physician, in London, where he was successively appointed assistant-physician to the Carey Street Dispensary, and physician to the City Dispensary. In 1799, he married a Miss Haldimand, the daughter of a merchant; in the following year he was naturalized, by a special act of parliament; and, in 1802, succeeded Dr. Harvey, as one of the physicians to Guy's Hospital. Although he strictly performed the duties attached to his public situation, and took notes of the principal points which occurred to him, both in hospital and private cases, he found time to render himself eminent

as a chemist, particularly for "his skill in analytical researches, and his extreme precision in the mode of conducting them." His talents procured for him the office of chemical lecturer, in conjunction with Mr. Allen, at Guy's Hospital, the reputation of which he helped greatly to establish in that department. In 1809, at the time of the Walcheren fever, having volunteered his services to the infected troops, he was appointed superintendent of the General Military Hospital at Portsmouth, where, after a zealous performance of his hazardous duties, he was himself taken ill, and, with difficulty recovered. A short while afterwards, a large fortune being left him by his father-in-law, he retired from practice, continuing, however, his chemical lectures at Guy's Hospital. a year after he had resigned his office of physician. In 1815, on the cessation of political troubles at Geneva, he visited that city, with his family, and remained there till 1821, having, in the meantime, been appointed a member of the Representative Council of Geneva, and professor of chemistry to its university. On his reaching England, he made a tour into Scotland; and, after returning to London, was making preparations to remove with his family to Geneva, when he was attacked with gout in the stomach, and died on the 9th of October, 1822. Dr. Marcet possessed a high reputation at the time of his death, both here and on the continent; and the indefatigable exertions he used in the promotion of science, and all objects of public utility, made him much esteemed and lamented. He rendered material service to the medical school at Guy's Hospital; procured for the patients there an amelioration of their diet, and introduced the plan of clinical lectures. In conjunction with Dr. Yelloly, he established the Medical and Chirurgical Society of London materially promoted the objects of the Royal Society, Geological Society, Royal Institution, and Northern Dispensary; and was chiefly instruniental in obtaining, from parliament, a grant for the support of the London Fever Hospital. From 1799, up to the year in which he died, he continued to contribute to the various periodical journals, and Transactions of learned societies, a number of papers on chemical

and medical subjects. They amount to nearly forty, and have been considered as valuable additions to science, and afford, at the same time, a proof of the rectitude of his judgment, and the variety of his talents. He was a most fortunate man, both in his profession and circumstances: "It was his lot," says his biographer, "to be placed in a situation peculiarly calculated to insure happiness." He was cheerful, benevolent, and had a keen relish for the enjoyments of life, which he was able, as well as desirous, to procure; and was endeared, by the excellence of his heart, the warmth of his affection, and high sense of honour, to a wide circle of friends, in whose society, it was observed, "his death left a mournful and irreparable chasm."

BIRKBECK, (GEORGE,) was born about the year 1770, and educated for the medical profession; but is chiefly eminent as the founder of the Mechanics' Institute, an establishment having for its object the diffusion of scientific knowledge among the lower orders. This laudable design had been entertained by Dr. Birkbeck as early as the year 1800, when he announced, at Glasgow, where he was professor in the Anderson College, a course of lectures on natural philosophy, and its application to the arts, for the instruction of mechanics. The extraordinary perspicuity of his method of teaching, the judicious selection of his experiments, and the natural attractions of the subject, combined to draw together very numerous audiences, composed, chiefly, of men who now, for the first time, were made acquainted with the principles of those operations, in directing or witnessing which, they had spent the greater period of their lives. Notwithstanding, however, the success with which these lectures met, it was twenty years before the experiment was repeated in any other town; a fact which is attributed, by a writer in The Edinburgh Review, to "the founder of the system having somewhat gone before the age." However, in 1821, lectures, upon the mode of Dr. Birkbeck's plan were established in Edinburgh, and with some material improvements. Upon this plan of the institution, the London one and all others have been founded; and a short

futation of Atheism, from the Laws of the Heavenly Bodies; and, On the Hypotheses accounting for gravitation from mechanical principles.

DODD, (RALPH,) was born in the county of Northumberland, about the year 1775, and came to London, in his sixteenth year, to study painting at the Royal Academy. He had also some employment at the London Docks; and after having prepared himself, in other ways, to carry on the business of a civil engineer, returned to his native county. In 1798, he again visited London, for the purpose of laying before government his plan for a tunnel under the Thames; which scheme, since entered upon by Mr. Brunel, was approved of, but abandoned soon after its commencement, from the operation of circumstances out of the control of the engineer. About the same time, Mr. Dodd obtained an act of parliament for making a canal between Gravesend and Chatham, to unite the rivers Thames and Medway by a nearer navigation than previously existed. The South Lambeth Water-works, the Grand Surrey Canal, the East London Waterworks, and Vauxhall Bridge, were projected by him; and he was the first who gave an impetus to steam navigation in England, by ailing round the coasts of England and Ireland in a steam vessel. An accident which he met with in one of these vessels, from the explosion of the boiler, proved fatal to him: after ingering some months, he died at Cheltenham, in April, 1822. In the various public works planned by Mr. Dodd, he displayed great ingenuity: but, says his biographer, a fluctuating temper and warmth of manner sometimes precluded the execution of his schemes, and thus prevented him from enriching himself or his family by his exertions. His works are, An Account of the Principal Canals in the known World, with Reflections on the great Utility of Canals; and Letters on the Improvements of the Port of London, without making Wet Docks.

BROWN, (THOMAS.) was born on the 9th of January, 1778, at Kirkmanbreck, in the stewartry of Kirkculdbright, of which his father was minister. The facility with which he learnt the

rudiments of education is remarkable: he was perfect in all the letters of the alphabet in the first lesson, and displayed similar quickness in every succeeding step. After having been placed at several schools, at each of which he distinguished himself, he was, in 1792, entered a student of the University of Edinburgh, where his attention was first directed to metaphysical studies, by Dr. Currie, to whom he was introduced, in 1793. This gentleman lent him to read the first volume of Stewart's Elements of the Philosophy of the Human Mind, with which Brown was so delighted, that he immediately became one of Mr. Stewart's pupils. At the close of one of his lectures, he went up to him, though personally unknown, and modestly stated some difficulties which had occurred to him respecting one of the professor's theories. Mr. Stewart heard him with attention, and candidly confessed to him that he had just received a communication from the distinguished M. Prevost, of Geneva, containing a similar objection. From this time, the professor and his pupil contracted a friendship, which continued throughout their lives. At the age of nineteen, Mr. Brown assisted in founding a private society in Edinburgh, under the name of the Academy of Physics, interesting in the history of letters as having given rise to the publication of The Edinburgh Review, and to the early numbers of which the subject of our memoir contributed several well-written articles. In 1798, he published his Observations on the Zoonomia of Dr. Darwin; and, when it is considered that the greater part of these were written in his eighteenth year, bis biographer, perhaps, only does him justice, in saying it may be doubted, if, in the history of philosophy, there is to be found any work exhibiting an equal prematurity of talents and attainments. In 1803, after having gone through the usual course of medical study, he took his degree of M.D.; and, in the same year, published two volumes of his poems. They were followed by An Examination of the Principles of Mr. Hume respecting Causation, a work highly recommended by Dugald Stewart, and which Sir James Mackintosh is said to have pronounced the finest model in mental philosophy since Berkeley

and Hume. It reached a third edition a short time previous to the author's death, with so many additions and alterations, as almost to constitute a new work, under the title of An Inquiry into the Relation of Cause and Effect. In 1806, Dr. Brown entered into partnership with Dr. Gregory; but his philosophical pursuits continued to occupy much more of his time than he devoted to the practice of his profession. In 1808-9, he appeared, as Mr. Stewart's substitute, in the chair of moral philosophy; and filled it with such reputation, that, in the following year, he was appointed joint professor in that class. In 1814, he published a poem called The Paradise of Coquettes; and, subsequently, several other poetical effusions, for the most part, anonymously, though they generally met with a favourable reception. His health beginning to decline in the autumn of 1819, he found some difficulty in delivering his lectures in the following winter, on the conclusion of which he went to London, and from thence to Brompton, where he died, on the 2nd of April, 1820. After his death, were published his Lectures, which have gone through numerous editions, and upon which his famne, as a philosopher, chiefly rests. He was possessed, in an eminent degree, of that comprehensive energy, which, to use his own words, "sees, through a long train of thought, a distant conclusion; and separating, at every stage, the essential from the accessory circumstances, and gathering and combining analogies as it proceeds, arrives, at length, at a system of harmonious

truth."

BRANDE, (WILLIAM THOMAS,) was born about the year 1780, and has, of late years, rendered himself very eminent by his experiments in chemistry, of which science he is professor at the Royal Institution. He succeeded Sir Humphry Davy in that situation, having acted as assistant to that eminent man. Mr. Brande is an able experimentalist, but has made no brilliant discoveries, nor is his elocution, as a lecturer, equal to that of his predecessor.

He has, however, acquired a high and merited reputation, and science is indebted to him for some very accurate and useful elementary books on chemistry and mineralogy. He also edited, for many years, a quarterly scientific journal, with great ability. His works are, Outlines of Geology; A Manual of Chemistry; Observations on an Astringent Vegetable Substance from China; A Dissertation, exhibiting a general view of the progress of Chemical Philosophy; and A Descriptive Catalogue of the British Specimens deposited in the Geological Collections of the Royal Institution.

DODD, (GEORGE,) son of Ralph Dodd, whose memoir we have previously given, was born about the year 1783. He was the original designer of Waterloo Bridge, to which he was appointed resident engineer, with a salary of £1,000 a-year; which situation he, however, thought proper to resign. He then engaged in the building of steamboats and other speculations; the failure of which is supposed to have affected his intellect. Being found, one night, intoxicated in the streets, he was placed in Giltspur Street Compter, where he died, about a week after, on the 25th of September, 1827.

SADLER, (WILLIAM WINDHAM,) born in 1796, possessed no mean abilities as a chemist and engineer, but is chiefly celebrated for his aerostatical experiments, to which he at length tell a victim. After having made thirty aërial voyages, in one of which he crossed the Irish channel, he ascended from the neighbourhood of Blackburn, in Lancashire, on the 30th of September, 1824, when the balloon, in its descent, striking against a chimney, he was thrown out of the car, from a very considerable height, and so severely injured, that his death soon followed. At the period of his death, he was resident at Liverpool, in the employ of the first gas company established there, and he had also opened an establishment for the use of warm, medicated, and vapour baths.