Pièce 17 - James David Forbes to William Whewell

4 pp

Edinburgh - Due to his 'First Six months Course' of lectures he has been neglecting his correspondence. Consequently he has not given enough time to WW's paper on Dynamical laws to offer a qualified opinion. In the course of the summer JDF prepared a treatise on mechanics that would 'have almost required a 6 months course to go through with nothing else'. His syllabus which he sent WW via Henslow [John Henslow], had the objective 'to impress general methods than to stave the memory with particular cases to train the mixed rather than give the practical details which are better learned from new books'. Further to WW's paper: In general he thinks 'we are much at one'. WW accedes to JDF's 'views in what I think an important point the derivation of the proportionality of Velocity to Force, - that force being measured by Statical methods with which the student is presumed to be familiar; which gave what I called the measure of a "definite amount of force" which expression you may remember you objected to'. He approves of WW's explanations about vis viva and the division of the necessary and contingent part of the laws: However, 'I would venture to suggest a change in the expression of your 3rd law which I think you are unwilling to let escape from Newton's Third, though I am quite convinced that his 3rd was your 3rd axiom, and that your third is part of his 2nd'. The subject of Rotation and Dynamics is 'ably treated in an elementary way in a work you should see, Dr. Jackson (of St Andrew's) mechanics I use it as a supplementary to your mechanics with my advanced pupils'.