Note 761 — Chapter V · (continued 2)

‘So much was he convinced of this, that he taught the doctrine in his lectures in 1761, before he had made a single experiment on the subject.’ … ‘The requisite experiments were first attempted by Dr. Black in 1764.’ Thomson's History of Chemistry, vol. i. p. 324. See also pp. 319, 320; and on the history of the idea in Black's mind as early as the year 1754, see the interesting extracts from his note-books in Robison's appendix to Black's Lectures, vol. i pp. 525, 526.

The statement of Dr. Thomson refers to the completion, or last stage, of the discovery, namely the vaporific combination of heat. But from a letter which Black wrote to Watt in 1780 (Muirhead's Life of Watt, London, 1859, p. 303), it appears that Thomson has even understated the question, and that Black, instead of first teaching his theory in 1761, taught it three years earlier, that is, six years before the decisive experiments were made. ‘I began,’ writes Black, ‘to give the doctrine of latent heat in my lectures at Glasgow in the winter 1757–58, which, I believe, was the first winter of my lecturing there; or if I did not give it that winter, I certainly gave it in the 1758–59; and I have delivered it every year since that time in my winter lectures, which I continued to give at Glasgow until winter 1766–67, when I began to lecture in Edinburgh.’