Page:A biographical dictionary of eminent Scotsmen, vol 9.djvu/300

564 nection with the bank of Leith. In session 1704-5 he began the study of medicine, and in 1795 resided in Edinburgh with his elder brother, afterwards the Rev. James Thomson, D.D., and still (1855) minister of the parish of Eccles, author of many articles in the "Encyclopaedia," and of works on the Gospel by St. Luke and Acts, and who succeeded the late Bishop Walker as colleague to Dr. (afterwards Bishop) Gleig, in the editorship of the "Encyclopædia Britannica." In the session of 1795-6 Dr. Thomson attended the lectures of the celebrated Dr. Black, of whom he always spoke in terms of the utmost veneration, and of gratitude for those invaluable instructions which first awoke the latent taste for the science of which he was destined to become so bright an ornament. In this session he wrote the article "Sea" for the "Encyclopædia." In November, 1796, he succeeded his brother in the editorship of the third edition of the "Encyclopædia," and remained con- nected with it till 1800. It was during this period that he drew up the first outline of his "System of Chemistry," which appeared in the Supplement to the "Encyclopædia," under the articles Chemistry, Mineralogy, Vegetable Substances, Animal Substances, and Dyeing Substances. These all appeared before the 10th December, 1800, when the preface was published, in which it is stated, by Dr. Gleig: of the author "of these beautiful articles, a man of like principles with Dr. Robison, it is needless to say anything, since the public seems to be fully satisfied that they prove their author eminently qualified to teach the science of chemistry." During the winter session of 1800-1, he gave his first chemical course with fifty-two pupils. Hence he appears to have been before the public as a lecturer for the long period of fifty-two years, and, as he used latterly to say, he believed he had lived to be the oldest teacher in Europe.

It was in the article Mineralogy, written about 1798, that he first introduced the use of symbols into chemical science, universally acknowledged to be one of the most valuable improvements in modern chemistry. In this article he arranges minerals into genera, according to their composition. Thus his first genus is A, or alumina, under which are two species, topaz and corundum, in accordance with the analyses of the day. The second genus is A M C, comprising spinell, which, according to Vauquelin, contained alumina, magnesia, and chrome iron ore. The fourth genus is S, including the varieties of silica or quartz. The eighth genus is S A G, or silica, alumina, and glucina, including the emerald or beryl; and thus he proceeds throughout. In the editions of his "System," the first of which (a development of the original article in the Encyclopaedia) was published in 1802, he continued the same arrangement and symbols, and was thus not only the originator of symbolic nomenclature in modern chemistry, but was the first chemist to bring mineralogy systematically within the domain of that science. In the third edition of his "System," published in 1807, in illustrating the atomic theory of Dalton, and in his article on oxalic acid, in the Philosophical Transactions for 1808, he freely uses symbols. Berzelius, who appeared some years later on the chemical stage, being Dr. Thomson's junior by five years, published a work in 1814, in Swedish, in which he adopted the system of symbols used by Dr. Thomson, with some modifications (the introduction of Latin initials in certain cases), but he strictly "followed the rules for this purpose given by Thomson in his ’System of Chemistry,'" (ōch skall dervid fōlga en enledning som Thomson gitvit i an kemiska handbok). The work in which this passage occurs, enti-