Pièce 25 - James David Forbes to William Whewell

6 pp

Edinburgh - News on the tide observations being done in Scotland: 'I have seen Mr Dall, under whose directions they are made. They extend to the time of high water and the depth'. Observations are taken twice a day: 'The observer is confidential and well looked after and his watch regulated. I have looked over some of the Tables, and was sorry to find a great many figures put down verbatim from the almanack I presume however that this is only done when the observed and completed times sensibly agree, because no deception can be intended since in the observation book the computed and observed times are placed side by side and therefore detection is immediate'. JDF is writing a paper on the Pyrenean springs, their temperature and geological relations for the Royal Society of London. He hopes his work on their temperature proves to be a model for future observers. He hopes to have magnified the effects of polarized heat to an extent that they are beyond doubt. He adopted a technique suggested by George Airy for polarizing by reflection which although convenient and decisive, was inferior to his own method of polarizing via thin plates of mica inclined at the polarizing angle. JDF gives an example with dark heat, and another in which he substitutes the usual heated plate [he gives a diagram] with a tin box filled with boiling water. JDF's students are 'voraciously' reading WW's mechanics [An Elementary Treatise on Mechanics, 4th edn. 1833]: 'It is out of print; you must give us a new one'.