Pièce 39 - James David Forbes to William Whewell

4 pp

Edinburgh - JDF sends WW a memorandum of his experiments [no longer attached]: 'Of the unexpected effect of Roughened surfaces there cannot be the slightest doubt. But whether the fine lines drawn by the surface of salt correspond in their action exactly to opake wires, as in diffractive experiments on light, I am not prepared to say, and indeed so far as direct experiments go I have not found my anticipations altogether verified. Can you suggest any mode of action of ground surfaces which opake fibres would not produce, and which would be analogous to that of Coloration in the case of Light?' JDF has been making some experiments on the form of the elliptic vibrations of heat to verify some formula of Cauchy [A.L. Cauchy] which he sent JDF to test: 'The results seem to come out well - and by a graphical process I can readily project the ellipse, find the direction of the greater axis, the excentricity etc'. Vernon Harcourt has written to JDF on the subject of Watt and Cavendish: 'I certainly think he is bound for his own sake and that of the association to probe to the bottom...he writes me that he has got plenty and most conclusive' [a controversy concerning the work of Watt and Cavendish]. WW has probably seen the 'angry translation of Arago [Dominique Arago] published under the sanction of Mrs Watt. The Edinburgh Review is on the whole I think fair in its criticisms, which rather surprised me considering the evidence of the authorship and the alliance with Lord Brougham [Henry Brougham]'. Has WW or anyone seen 'Lord B's analysis of Newton's Principia?' Does WW 'think it necessary that the light or heat transmitted by an opake grating should always be as the Area of Interstices, independent of wavelength?'