88 Memoir of the late 



late Bishop Walker as colleague to Dr (afterwards Bishop) 

 Gleig, father of the present eminent Inspector of Army Edu- 

 cation, in the editorship of the " Encyclopaedia Britannica." 

 It was in the session of 1795-96 that 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 " Encyclopaedia." In November 1796, he suc- 

 ceeded his brother in the editorship of the Supplement to the 

 third edition of the " Encyclopaedia," and remained in this 

 position 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 " Encyclopaedia, 1 ' under 

 the articles Chemistry, Mineralogy, Vegetable Substances, 

 Animal Substances, and Dyeing Substances. These all ap- 

 peared 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 Bobison, 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.'' From 

 this authority we infer that it was during the winter session 

 of 1800-1 he first gave a chemical course. Hence, he ap- 

 pears to have been before the public as a lecturer for the 

 long period of fifty-two years, and, as he used lately to say, 

 he believed he lived to be the oldest teacher in Europe. 



1. 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 im- 

 provements in modern times. 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 Vanquelin, contained alumina, magnesia, and 

 chrome iron. The fourth genus is S, including the varieties 

 of silica or quartz. The eighth genus is SAG, or silica, 



