My Dear Sir,
Having returned only yesterday from Slough, <1> I have been prevented from returning you my best thanks for the beautiful Prism which you have been so kind as to give me.<2> It will enable me to complete a series of Experiments on the absorption of the heat of the spectrum <3> by transparent and other media, during which I have obtained several curious and unexpected results.
I earnestly hope that you will go on with your own optical researches. Your leisure, and powers of original investigation are capable of doing much for Science; and it would give me the greatest pleasure to receive occasionally a notice of what you have done.
I am My Dear Sir Ever Most Faithfully yrs
24 Sussex Place
July 1st 1831
1. Sir John Herschel recorded in his diary on 29 June 1831: ‘Dr Brewster came to Slough & passed the rest of the day with me.’ Just three days before, on 26 June, Herschel, WHFT and Brewster were at a breakfast at Professor Charles Babbage’s (1792–1871), mathematician & inventor. Quite possibly Herschel’s demonstration of the light-sensitivity of platinum salts at this breakfast was one of the ‘floating philosophical visions’ that WHFT felt might have triggered his quest for photography. See Larry J. Schaaf, ‘Herschel, Talbot, and Photography; Spring 1831 & Spring 1839’, in History of Photography, v. 4 no. 3, July 1980, pp. 181–204.