Pièce 15 - James David Forbes to William Whewell

4 pp

Edinburgh - Thanks WW for his attention regarding JDF's comments on Dynamics [see JDF to WW, 20 July 1833]. JDF feels a strong need 'to satisfy myself as to the essential aspects of the substructure of Dynamics which I do think has in general been most loosely done'. A student must get very confused sifting the essentials of Dynamics: 'I think great confusion has arisen by introducing at once the phrases Accelerating and Moving Force, instead of explaining as Newton does that this is merely a contraction for 'Accelerating Effect of a force' 'moving effect of a Force''. Accelerating force is characterised by the velocity produced - it has no existence. JDF does not think WW improves the abuse of Force by introducing the term pressure. JDF gives a list of definitions which he considers the clearest way of showing the connection of the Principles of Dynamics and their origin: He would like WW to draw up a half page of some similar list of definitions. Has WW 'got the new edition of Poisson's mechanique [S. D. Poisson, Traite de Mechanique, 1st edn. 1811] you will find that so far from converting him about the 3 Laws he has cut his two down to one! viz the law of Inertia deducing everything else a priori'.