appointed lecturer on chemistry in Glasgow university. Hitherto this science had been only treated as a curious, and, in some respects, a useless art. This great man, conscious of his own strength, and taking a wide and comprehensive view, saw the unoccupied field of philosophical chemistry open before him. He was satisfied that it was susceptible of great improvement, by means of liberal inquiry and rational investigation. It was perhaps the good fortune of Dr Black, in falling under such a master, that gave his mind a peculiar bent in favour of this department of physical science. His previous acquirements and extraordinary aptitude speedily became known to Dr Cullen, who was at all times remarkable for the personal attentions he paid to his pupils. Black became a valuable assistant to Dr Cullen in his chemical operations, and his experiments were sometimes publicly adduced in the lecture, as a sufficient authority for various new facts. Thus commenced a friendship between two great men, which was never afterwards interrupted, except by the Great Divider of kindred minds and loving hearts, and which was of considerable service to mankind.
In 1751, Black was sent to Edinburgh to complete the course of his medical studies. At this time, the mode of action of lithotriptic medicines, but particularly lime water, in alleviating the pains of stone and gravel, divided the opinions of professors and practitioners. This subject attracted the attention of Black, and it appears from some of his memorandums, that he at first held the opinion, that the causticity of alkalis was owing to the igneous matter which they derive from quick lime. Having prosecuted his experiments on magnesia, the grand secret of nature, which for ever will be associated with his name, was laid open to him. He perceived that the acrimony of these substances was not owing to their combination with igneous particles; that it was their peculiar property; and that they lost this property, and became mild, by combining with a certain portion of air, to which ha gave the name of fixed air; because it was fixed or become solid in the substances, into the composition of which it entered. He discovered, for instance, that a cubic inch of marble consisted of half its weight of pure lime, and a quantity of air equal to six gallons measure. This grand discovery, which forms one of the most important eras of chemical science, was the subject of his inaugural essay, on obtaining his degree as doctor of medicine; and the reputation it acquired for him, was the means, in 1756, of placing him in the chair of chemistry at Glasgow, then vacated by Dr Cullen, who was transferred to the same chair in the college of Edinburgh. The theory of fixed air (now termed by chemists, carbonic acid gas,) was speedily propagated on the continent, where at this time chemistry was occupying the attention of many great men. In Germany, Dr Black's opinions, though placed on the firmest basis by experiments, met with much opposition, which, it appears, gave him an uneasiness not to have been expected from his philosophical, and rather indolent character. In France, however, he was very differently treated. Lavoisier, in sending him a copy of his treatise on respiration, thus expressed himself: "It is but just you should be one of the first to receive information of the progress made in a career which you yourself have opened, and in which all of us here consider ourselves your disciples." To this Black replied, with a just admiration of what the French chemists were doing, and without reference to any merit of his own.
On his assuming the chair of chemistry at Glasgow, that of anatomy was also imposed upon him; but this latter he soon exchanged for that of medicine, for which, it would appear, he was better qualified. He gave great satisfaction by the perspicuity and simplicity, the caution and moderation, which he discovered in his medical lectures. At the same time, he became a favourite practitioner in the city, where his engaging appearance and manners, and the benevolent and unaffected interest which he took in all the cases entrusted to his care, ren-
