In reference to this period, it has been sometimes remarked as singular, that while chemical science was beginning to make those rapid strides by which its modern advance has been so much accelerated, Dr. Black should have been contented to go on merely as an able expositor and illustrator of what others were doing, without himself taking any share in their labours. Perhaps it might be difficult to assign any better reasons for this conduct than are to be found in the peculiar disposition of the individual, though it has been alleged that he was actuated by a dread of criticism; this, indeed, can only be regarded as itself an indication of a morbid sensitiveness of mind, of which, unhappily, we have other instances in individuals of the highest philosophical genius; and which has probably, in more than one instance, deprived the world of services which would have been invaluable in the cause of science. Be this as it may, Dr. Black, though he continued by constant revisions and additions to make his lectures amply keep pace with the discoveries of the day, yet himself produced during this period only two papers, and those of minor importance: one appeared in the Philosophical Transactions for 1774, in which he assigned the reason why water which has been boiled freezes more easily than that which has not, viz., the expulsion of the air: another was inserted in the second volume of the Edinburgh Transactions, on the analysis of the water from the Geysers of Iceland. It appears from an anecdote related on good authority, (see Edinburgh Encyclopædia, article, Dr. Black) that so early as 1766, when the low specific gravity of hydrogen as discovered by Mr. Cavendish had been announced, the idea of employing it for balloons occurred to Dr. Black; and that he actually exhibited a small one, to the extreme astonishment of a party of friends. It was not till 1782 Montgolfier claimed the merit of originating this idea. Dr. Black never enjoyed very robust health, but by great care and attention he managed to the best advantage a constitution naturally delicate, pursuing, especially towards the latter part of his life, an extremely regular and abstemious mode of living. About 1793 his strength began to fail. In 1796 he became unequal to the sole discharge of his duties as a lecturer, and employed an assistant. In the following year he was compelled to relinquish lecturing altogether. Though in great weakness, he was able by unremitting precautions to preserve a considerable share of general health. He had always expressed a hope that he might be spared the distress of a long illness; and, in accordance with this wish, while sitting at table partaking of his usual simple fare, he expired November 26, 1799, in so tranquil a manner, that a cup of milk which he had placed on his knee remained unspilt; and it was some time before his servant perceived that life was extinct.