Pièce 40 - James David Forbes to William Whewell

5 pp

Edinburgh - JDF returns the proof sheets on heat which WW sent him to check [a section of WW's The Philosophy of the Inductive Sciences, Founded upon their History ?]. WW has no doubt seen Dominique Arago's unimpressed 'Interim reply' to Vernon Harcourt [see JDF to WW, 8 Feb. 1840]. JDF has 'not quite (but nearly) done tormenting heat with gratings and Dusty Diaphragms. All I can do, all kinds of Heat get through the finest gratings (metallic) in precisely equal proportions and that equal to the area of Interstices; yet grooved surfaces exert a powerful specific action. I am reluctantly forced to the conclusion too, that pure metals may be reduced to powder so fine as to affect the quality of the heat transmitted, tho' the thinnest gold leaf prevents no appreciable portion of heat to pass'.