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. During above thirty years he inculcated the elements of chemistry upon enthusiastic and continually growing audiences. ‘It could not be otherwise,’ Robison wrote in 1803. ‘His personal appearance and manner were those of a gentleman, and peculiarly pleasing. His voice in lecturing was low, but fine; and his articulation so distinct that he was perfectly well heard by an audience consisting of several hundreds. His discourse was so plain and perspicuous, his illustrations by experiment so apposite, that his sentiments on any subject never could be mistaken, even by the most illiterate; and his instructions were so clear of all hypothesis or conjecture, that the hearer rested on his conclusions with a confidence scarcely exceeded in matters of his own experience’ ( Lectures, preface, lxii). His lectures had thus a powerful effect in popularising chemistry; and attendance upon them even came to be a fashionable amusement.

Black was a prominent member of the intellectual society by which Edinburgh was then distinguished. Amongst his intimates were his relative and colleague Adam Ferguson, Hume, Hutton, A. Carlyle, Dugald Stewart, and John Robison. Adam Smith, with whom he knit a close friendship at Glasgow, used to say that ‘no man had less nonsense in his head than Dr. Black.’ He was one of James Watt’s earliest patrons, and kept up a constant correspondence with him, Though grave and reserved, Black was gentle and sincere, and it is recorded of him that he never lost a friend. He was at the same time gifted with a keen judgment of character, and with the power of expressing that judgment in an ‘indelible phrase.' In person he is described as ‘rather above the middle size; he was of a slender make; his countenance was placid, and exceedingly engaging’. As he advanced in years, Robison tells us, he preserved a pleasing air of inward contentment. Graceful and unaffected in manner, ‘he was of most, easy approach, affable, and readily entered into conversation, whether serious or trivial.’ Nor did he disdain elegant accomplishments. In his youth he both sang and played tastefully upon the flute. He had talent for painting, and ‘figure of every kind excited his attention even a retort or a crucible was to his eye an example of beauty or deformity.' But love of propriety, the same authority informs us, was his leading sentiment, Indeed, his mind was so nicely balanced as to be deficient in motive power. He had all the faculties of invention, but lacked fervour to keep them at work. Hence the slackness with which he pursued discoveries which his genius, as it were, compelled him to make.

A perhaps more prevailing reason for his inaction was the weakness of his constitution. The least undue strain, whether physical or mental, produced spitting of blood, and it was only by the most watchful precautions that he maintained unbroken, though feeble, health. From 1793, however, it visibly declined, and he led, more and more completely, the life of a valetudinarian. In 1795 Charles Hope was appointed his coadjutor in his professorship; in 1797 he lectured for the last time. The end came 6 Dec. 1799 (, in Proc. Royal Soc. Edinburgh, ii. 238), just in the way he had often desired. ‘Being at table,’ Ferguson relates, ‘with his usual fare, some bread, a few prunes, and a measured quantity of milk diluted with water, and having the cup in his hand when the last stroke of the pulse was to be given, he appeared to have set it down on his knees, which were joined together, and in the action expired without spilling a drop, as if an experiment had been purposely made to evince the facility with which he departed.’ The provisions of his will curiously illustrated the just but cold precision of his modes of thought. He divided his property, without specification of its amount, into 10,000 portions, ‘parcelled to a numerous list of relatives, in shares, in numbers or fractions of shares, according to the degree in which they were proper objects of his care or solicitude.’ He was never married, but lived on the best terms with his family. His morals were irreproachable, his habits abstemious, his frugality was free from parsimony. Indifferent to fame, he disliked the publicity of authorship, and never could be induced to vindicate claims which his friends held to be, in many quarters, encroached upon. He enjoyed, nevertheless, a unique reputation. Fourcroy called him ‘the Nestor of the chemistry of the eighteenth century’ (, Hist. de la Chimie, ii. 353); Lavoisier acknowledged himself his disciple, Black, on his side, while professing the highest admiration for Lavoisier's genius, and admitting his discoveries, intensely disliked what he regarded as his premature generalisations. ‘Chemistry,' he observed, ‘is not yet a science. We are very far from the knowledge of first principles. We should avoid everything that has the pretensions of a full system’ (Lectures, note xxvi.) This philosophic caution was eminently characteristic.

Amongst other honours Black was elected member of the Paris and St. Petersburg Academies of Sciences, of the Society of Medicine of Paris, as well as of the Royal Society