The concepts and theories of modern physics / By J.B. Stallo.

  • John Stallo
Date:
1900
Catalogue details

Licence: In copyright

Credit: The concepts and theories of modern physics / By J.B. Stallo. Source: Wellcome Collection.

    126/376 (page 76)
    due to Huygens, and is in these words: “ The quantity of motion possessed by two bodies may be augmented or diminished by their encounter; but there remains always the same quantity on the same side, if we sub- tract the quantity of opposite motion. . . . The sum of the products of every hard body multiplied by the square of its velocity is always the same before and after the encounter.”* The progress made up to this point, in the rectili- cation of the Cartesian doctrine, consisted in the denial of the conservation of motion in the sense of mere velocity or of the quantity of motion and the rate of its change irrespective of its direction, and in the asser- tion of the conservation of energy of motion—a quan- tity proportional to the product of mass into the square of its velocity. Such was the state of the doctrine in Newton’s time. The Leibnitian principle might, even at this time, (all the premisses being given in Newton’s laws of mo- tion, and especially in his interpretation of the third law) have been generalized so as to embrace, or to im- * “ La quantity du inouvement qu’ont deux corps sc peut augmenter ou diniinuer par Icur rencontre; niais il y reste toujours la memo quan- tite vers le memc cote, en soustrayant la quantity du mouvement con- traire .... La soinme des produits faits de la gi’andeur do chaque corps dur raultiplid par Ic quarrd do sa vitesse, est toujours la meuae devant et aprds la rencontre.” Cf. Akin, “ On the History of Force,” Phil. Mag., 4th scries, vol. xxviii, p. 472. Professor Bohn’(ift., p. 313) claims the honor of priority in giving a clear exposition of the principle of the conservation of v?s viva for .John Bernoulli; but upon perusal of the passages quoted by him it will be seen that Bernoulli’s conception rested upon the metaphysical assumption of the substantiality of motion and the equality of cause and effect. Indeed, John Bernoulli had adopted the principle in the form and upon the considerations presented by Leib- nitz, who, like Descartes, was a metaphysician rather than a physicist, while Huygen.s, a true man of science, arrived at his propositions by a series of generalizations of special cases.