Pièce 49 - James David Forbes to William Whewell

4 pp

Chamouni - George Airy has probably told WW of 'the fate of the Eclipse [from Turin] which for me at least was as nearly a failure as the circumstances admitted'. JDF has tried to put an end to his controversy with Louis Agassiz [see JDF to WW, 23 May 1842], however, Agassiz 'replied very coldly declining to see me'. JDF has been well received by Studer [Bern. Studer], Charpentier [Jean de Charpentier] and his other Geneva friends, and his controversy with Agassiz has 'in general here as well as in Paris ...been correctly enough interpreted'. He has been able to 'establish many things about the movement of glaciers which so far as I know have never been solved directly': It is a physico-mechanical question: Does a glacier move uniformly at all its points of its length and breadth? Does it move at all seasons? From the measurements he has already made, JDF thinks that the glaciers movement probably depends on the temperature: 'Nevertheless the variation of day and night scarcely modifies the glaciers march. Whilst, hitherto, the proof of glacier motion has been watching the progress of a block of stone from year to year by some rough measurement from a fixed point, I have constructed a glacier dial on the face of a Rock, on which it not only apparently 'moved from day to day' - but on which I can trace its march from hour to hour!'. A glacier moves slower the nearer it is to its origin as opposed to its extremity, and fastest at the centre of its breadth: 'contrary to the opinion hitherto universally entertained that the edges move fastest'. The circumstances of the movement of a glacier (in all its points) can be determined in a few days at a particular season. He has made a number of observations of the veined structure of ice glaciers: no one had 'imagined that structure existed generally, until my paper was published'.

Letter torn on right margin of both leaves, affecting much text.