WILLIAM HENRY, M.D., F.R.S., &c.

Born December 12, 1774. Died September 2, 1836.

Dr. William Henry, the distinguished chemical philosopher, was born at Manchester. His father, Mr. Thomas Henry, was a zealous cultivator of chemical science. The earliest impressions of Henry's childhood were, therefore, such as to inspire interest and reverence for the pursuits of science; and he is said, when very young, to have sought amusement in attempting to imitate, with such means as were at his disposal, the chemical experiments which his father had been performing. A severe accident which occurred in early life, by disqualifying him for the active sports of boyhood, also contributed to determine his taste for books and sedentary occupations. This injury, occasioned by the fall of a heavy beam upon his right side, was of a very serious nature, and materially checked his growth; it left as its consequence acute neuralgic pains, which recurred from time to time, with more or less severity, during the remainder of his life.

Dr. Henry's earliest instructor was the Rev. Ralph Harrison, who possessed considerable repute as a teacher of the ancient languages, and was considered at that period to be one of the best instructors of youth in the North of England. Immediately on leaving Mr. Harrison's academy at Manchester, Henry had the good fortune to become the private secretary of Dr. Percival, a physician of great general accomplishments and refined taste, whose example and judicious counsels were most instrumental in guiding the tastes of his young companion, and in establishing habits of vigilant and appropriate expression. In this improving residence Dr. Henry remained for the space of five years; he was then removed, in the winter of 1795-6, to the University of Edinburgh, after having acquired some preliminary medical knowledge at the Infirmary at Manchester. Prudential considerations compelled him to leave the University at the end of a year, and commence general medical practice in company with his father. A few years' experience, however, showed the inadequacy of his delicate frame to bear up against the fatigues of this branch of the medical profession, and he was permitted, in the year 1805, to return to the University, at that time adorned by the learning of Playfair and Stewart. So powerful was the stimulus given to his mental powers during his residence at the University, that he often declared that the rest of his life, active as it was, appeared a state of inglorious repose when contrasted with this season of unremitted effort. The period intervening between Dr. Henry's two academic residences, although passed in the engrossing occupations of his profession, to which was added the superintendence of a chemical business previously established

by his father, was yet marked by several important contributions to science. In 1797 he communicated to the Royal Society an experimental memoir (the first of a long series with which he enriched the Transactions' of that body), the design of which was to re-establish the title of carbon to be ranked among elementary bodies, which had been denied by Austin, Beddoes, and other eminent chemists. In this paper he subsequently discovered a fallacy in his own reasoning, which he exposed before it had been detected by any other chemist. In 1800 he published in the 'Philosophical Transactions' his experiments on muriatic acid gas, and in 1803 made known to the Royal Society his elaborate experiments on the quantity of gases absorbed by water at different temperature and under different pressures, the result of which was the establishment of the law that "water takes up of gas, condensed by one, two or more additional atmospheres, a quantity which would be equal to twice, thrice, &c. the volume absorbed under the ordinary pressure of the atmosphere." In 1808 Henry was elected a Fellow of the Royal Society, and in the same year described in their 'Transactions' a form of apparatus adapted to the combustion of larger quantities of gases than could be fired in eudiometric tubes. This apparatus, though now superseded, gave more accurate results than had ever before been attained. In the following year (1809) the Copley gold medal was awarded to him for his valuable contributions to the 'Transactions' of the Royal Society. For the next fifteen years Dr. Henry continued his experiments on gases, making known to the Society the results from time to time. In his last communication, in 1824, he claimed the merit of having conquered the only difficulty that remained in a series of experiments on the analysis of the gaseous substances issuing from the destructive distillation of coal and oil-viz., the ascertaining by chemical means the exact proportions which the gases, left after the action of chlorine on oil and coal gas, bear to each other. This he accomplished by skilfully availing himself of the property (recently discovered by Döbereiner), in finely divided platinum, of causing gaseous combinations, and he was thus enabled to prove the exact composition of the fire-damp of mines. All the experiments of Dr. Henry which have been previously alluded to bore upon äeriform bodies; but although these were his favourite studies, his acquaintance with general chemistry is proved by his 'Elements of Experimental Chemistry,' to have been both sound and extensive. This work was one of the first on chemical science published in this country, which combined great literary elegance with the highest standard of scientific accuracy. His comparative analysis of many varieties of British and foreign salts were models of accurate analysis, and were important in dispelling the prejudices then popular in favour of the latter for economical purposes. His 'Memoir on the Theories of Galvanic Decomposition' earned the cordial approval of Berzelius, as being

among the first maintaining that view which he himself so earnestly supported.

It is greatly to be regretted that Dr. Henry did not contribute more to the literature of science, as he appears to have been eminently fitted, both by natural tastes and by after culture, to excel in this particular respect; especially is it to be regretted that he did not live to carry out the great literary project for which he had collected materials—a history of chemical discovery from the middle of the last century. He could have made it one of the most popular books in our tongue.

In the general intercourse of society Dr. Henry was distinguished by a polished courtesy, by an intuitive propriety, and by a considerate forethought and respect for the feelings and opinions of others; qualities issuing out of the same high-toned sensibility, that guided his taste in letters, and that softened and elevated his whole moral frame and bearing. His comprehensive range of thought and knowledge, his proneness to general speculation in contradistinction to detail, his ready command of the refinements of language, and the liveliness of his feelings and imagination, rendered him a most instructive and engaging companion. To the young, and more especially to such as gave evidence of a taste for liberal studies, his manner was peculiarly kind and encouraging. In measuring the amount and importance of his contributions to chemical knowledge, it must be borne in mind, that in his season of greatest mental activity, he never enjoyed that uncontrolled command of time and that serene concentration of thought which are essential to the completion of great scientific designs. In more advanced life, when relieved from the duties of an extensive medical practice and other equally pressing avocations, growing infirmities and failing bodily power restrained him to studies not demanding personal exertion, and even abridged his season of purely mental labour. That amid circumstances so unfriendly to original and sustained achievements in science, he should have accomplished so much, bears testimony to that energy of resolve, that unsubdued ardour of spirit which ever glowed within him, urging him steadily onwards in the career of honourable ambition, and prompting exertions more than commensurate with the decaying forces of a frame that had never been vigorous. At intervals during his whole life, Dr. Henry suffered severely from the effect of the accident already mentioned. The paroxysms of intense neuralgic agony which attacked him, at length caused the whole nervous system to be so irritated as to deprive him of sleep, and cause his death in September, 1836, at the age of sixty-one. Biographical Account of the late Dr. Henry, by his son, William Charles Henry, M.D., F.R.S., &c.—Encyclopædia Britannica, Eighth Edition.

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SIR WILLIAM HERSCHEL, D.C.L., F.R.S., &c.

Born November 15, 1738. Died August 23, 1822.

Authentic particulars respecting both the early and private life of this great astronomer are sadly deficient; his scientific works are, however, of a world-wide reputation, and it is with these that we are chiefly concerned. William Herschel was born at Hanover, and was one of a numerous family, who supported themselves chiefly by their musical talents. At the age of fourteen William was placed, it is said, in the band of the Hanoverian regiment of Guards, which he accompanied to England at a period variously stated from 1757 to 1759. On his arrival he remained for some time at Durham, and was subsequently, for several years, organist at Halifax, where he was also employed in teaching music and studying languages. At length, about the year 1766, he found himself in comparatively easy circumstances, as organist of the Octagon Chapel at Bath. Here Herschel began to study earnestly the science of astronomy; and feeling the necessity of obtaining a good telescope, the purchase of which would be beyond his means, he determined to make one himself. After many trials, he succeeded in 1774 in executing with his own hands a reflecting telescope, and soon acquired so much dexterity, as to construct instruments of ten and twenty feet in focal length.

In the year 1780 he contributed his first paper, 'On the Variable Star in Cetus,' to the Royal Society; and on the 13th of March, 1781, announced to the world his discovery of a supposed comet, which, on further examination, proved to be a planet exterior to Saturn, now named Uranus.* This fortunate success was the first addition to the number of primary planets since a period of an immemorial antiquity, and it speedily made the name of Herschel famous.

George III. took the new astronomer under his protection, and attached him to his court, bestowing on him the title of astronomer to the king, with a salary of 400l. a year. It is difficult to estimate the amount of benefit thus conferred on astronomy by the award of this pension; for nothing short of the entire devotion of a lifetime, could have produced such results as we owe to Herschel. His contributions to the 'Philosophical Transactions' alone amount to sixty-nine in number, and may give some idea of the unwearied activity of the author; they range over a period of thirty-five years, commencing in 1780 and terminating in 1815. The numerous bodies which he added to the solar system, make that number half as large again as he found it. Including Halley's comet, and the four satellites of Jupiter and five of Saturn, the number previously known

* Called at first Georgium Sidus in honour of George the Third.

was eighteen, to which Herschel added nine-namely Uranus and six satellites, and two satellites of Saturn. His discovery of the rotation of Saturn's ring, his measurements of the rotation of Saturn and Venus, his observations of the belts of the former, and his conjectural theory-derived from observation-of the rotation of Jupiter's satellites, with a large number of minor observations, prove that no one individual ever added so much to the facts on which our knowledge of the solar system is founded. His leading discoveries in siderial astronomy include the discovery of binary systems of stars, and the orbits of several revolving stars; the discovery and classification of a prodigious multitude of nebula; the law of grouping of the entire firmament, and its connection with the great nebula of the Milky Way; and lastly, the determination of the motion of our sun and system in space, and the direction of that motion.

Herschel's magnificent speculations on the Milky Way, the constitution of nebulæ, &c., first opened the road to the conception, that what was called the universe was, in all probability, but a detached and minute portion of that fathomless series of similar formations which ought to bear the name. Imagination roves with ease upon such subjects; but before Herschel's observations, even that daring faculty would have rejected ideas which afterwards proved to be but sober philosophy. These great and arduous enquiries occupied Herschel during nearly the whole of his scientific career, extending to almost half a century, and, excepting the continuation of his labours by his illustrious son, Sir John, little has been added to our knowledge of the constitution of the heavens' since his death.

As an optician, Herschel deserves equal notice for the wonderful improvements which he effected in the dimensions and magnifying power of telescopes, and by the skill with which he applied them to celestial observations. The reflecting telescope was the one to the improvement of which he so successfully devoted himself; and the real secret of his success in this, was his astonishing perseverance; his determination being to obtain telescopes of twenty feet focal length or more, and of a perfection equal or superior to the small ones then in use. He himself relates, that whilst at Bath he had constructed 200 specula of seven feet focus, 150 of ten feet, and about 80 of twenty feet; a proof of extraordinary resolution in a man of limited means, and at that time engaged in a laborious profession.

Herschel at last succeeded in constructing his enormous telescope of forty feet focal length, which he erected in the grounds of his house at Slough. This instrument was begun in 1785, and finally completed on August 28th, 1789, on which day Herschel discovered with it the sixth satellite of Saturn; the diameter of the tube was 4 feet 10 inches, the speculum having a useful area of 4 feet: the