Two essays : one upon single vision with two eyes ; the other on dew : a letter to the Right Hon. Lloyd, Lord Kenyon, and an account of a female of the white race of mankind, part of whose skin resembled that of a negro ; with some observations on the causes of the differences in colour and form between the white and negro races of men / by the late William Charles Wells, with a memoir of his life, written by himself.

Date:
1818
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Licence: Public Domain Mark

Credit: Two essays : one upon single vision with two eyes ; the other on dew : a letter to the Right Hon. Lloyd, Lord Kenyon, and an account of a female of the white race of mankind, part of whose skin resembled that of a negro ; with some observations on the causes of the differences in colour and form between the white and negro races of men / by the late William Charles Wells, with a memoir of his life, written by himself. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    XI. Thinking it probable, that black bodies might radiate more heat to the sky, at night, than white, 1 placed upon grass, on five different evenings, equal parcels of black and white wool. On four of the succeeding mornings, the black wool M'^as found to have acquired a little more dew than the white ; whence I inferred that it had, in consequence of its colour, radiated a little more heat. But I afterwards remarked, that the white wool was somewhat coarser than the black; which circumstance alone was which were published, first in the 44th volume of the French Annals of Chemistry, and afterwards by Mr. Peter Prevost of Geneva, in his Essay on Radiant Heat; but fearing to be very tedious, I have since given up the design. I wdll say, however, that, if to what is now generally known on the different modes, in which heat is communicated from one body to another, be added the two following circumstances j that substances become colder, by radiation, than the air, before they attract dew; and that bright metals, when ex- posed to a clear sky at night, become colder than the air much less readily than other bodies j the whole of the ap- pearances observed by Mr. Prevost may be easily accounted for. Note to second edition.'] I found, shortly after the publica- tion of the former edition of this Essay, that the learned Dr, Young had, several years before, in his great work on Na- tural Philosophy, employed the principle of the radiation of heat to account for several of the facts observed by Mr. B. Prevost. On the subject of Dr. Young’s explanation, I have spoken somewhat fully in the 28th number of Dr. Thomson s Annals of Philosophy.