‘Mr. Stewart’s death affects me deeply. A sincere friendship, begun at twelve years of age, and continued to my time of life, without any interruption, cannot but give some pangs. You know his worth; yet it was shaded ever since you knew him by too great abstraction from the world. The former part of his life was more amiable and more social; but the whole was of a piece in virtue, candour, and humanity.... I have always regarded him as my best tutor, though of the same age with me. If the giddy part of my life was in any degree spent innocently and virtuously, I owe it to him more than to any human creature; for I could not but be virtuous in his company, and I could not be so happy in any other. But I must leave this pleasing melancholy subject. He is happy; and I shall often be happy in the remembrance of our friendship; and I hope we shall meet again.’ A minute account of Black’s theory of latent heat follows. Later in the same year, Black was called to the Chair of Chemistry in Edinburgh, which he filled for nearly thirty years, and in Reid’s letters to the Skenes there is much about candidates for the vacant office in Glasgow, with a suggestion that David Skene should himself enter the lists. ‘There is a great spirit of inquiry among the young people here. Literary merit is much regarded; and I conceive the opportunities a man has of improving himself are much greater here than at Aberdeen. The communication with Edinburgh is easy. One goes in the stage coach to Edinburgh before dinner; has all the afternoon there, and returns to dinner at Glasgow next day; so that if you have any ambition to get into the College of Edinburgh (which I think you ought to have), I conceive Glasgow would be a good step.’ The appeal was ineffectual. Meantime his own appointment, as an ‘examinator’ of candidates for the vacant Mathematical Chair in Marischal College, made a visit to Aberdeen necessary, as anticipated in a letter on ‘May 8th’:—