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Titre : Philosophical transactions of the Royal society of London : giving some accompt of the present undertakings, studies, and labours of the ingenious in many considerable parts of the world. VOL157 (1867)
Auteur : Royal society (GB). Auteur du texte
Éditeur : Royal societyRoyal society (London)
Date d'édition : 1665-1886
Notice d'ensemble : http://catalogue.bnf.fr/ark:/12148/cb37571969b
Type : monographie imprimée
Langue : anglais
Format : Microfiches ; 105*148 mm
Description : Collection numérique : Nutrisco, bibliothèque numérique du Havre
Droits : conditions spécifiques d'utilisation - Microformes et reprints
Droits : restricted use
Identifiant : ark:/12148/bpt6k559627
Source : Bibliothèque nationale de France
Conservation numérique : Bibliothèque nationale de France
Date de mise en ligne : 10/03/2009
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IV. On the Z~maMM'M? y/!<'0~ 0/ Gss~. -B~ J. CLERK MAXWELL, jF'<S'. L. ~-J? RcceivedMay'[6,–ReadMay31,1866.
THEORIES of the constitution of bodies suppose them either to be continuons and homogeneous, or to be composed of a finite number of distinct partides or molécules. In certain applications of mathematics to physical questions, it is convenient to suppose bodies homogeneous in order to make the quantity of matter in each differential element a function of the coordinates, but 1 am not aware that any theory of this kind has been proposed. to account for the different properties of bodies. Indeed the properties of a body supposed to be a uniform plenum may be amrmed dbgmatically, but cannot bc cxplained mathematically.
Molecular théories suppose that all bodies, even when they appear to our senses homogeneous, consist of a multitude of particles, or small parts the mechanical relations of which constitute the properties of thé bodies. Those théories which suppose that the molécules are at rest relative to the body may be called statical theories, and those which suppose thé molecules to be in motion, even while thé body is apparently at rest, may be called dynamical théories.
If we adopt a statical theory, and suppose the mpiecules of a body kept at l'est in their positions of equilibrium by thé action of forces in the directions of thé linesjoining their centres, we may determine the mechanical properties of a body so constructed, if distorted so that the displaçement of each molécule is a function of its coordinates when in equilibrium. It appears from thé mathematical theory of bodies of this kind, that the forces called into play by a small change of form must alwàys bear fixed proportion to those excited by a small change of volume.
Now we know that in fluids thé elasticitv of form is evanescent, while that of volume is considérable. Hence such theories will not apply to fluids. In solid bodies the elasticity of form appears in many cases to be smaller in proportion to that of volume than thé theory givcs*, so that we are forced to give up thé theory of molécules whose displacements are functions of their coordinates when at rest, even in the case of ~lid. bodies. a
Thé theory of moving molécules, on~h'e other Itand, is not open to thèse objections. Thé mathematical difficulties in applying the theory are considérable, and till they are surmouutedwc cannot fully décide on thé applicability. of the theory. We are a.ble, however, to explain a great variety of phenomena by the dynamical theory which have not been hithertoexplainedotherwise.
Thé dynamical theory supposes that the molecules of solid bodies oscillate aboutJLheit [In gluss, according to Dr. EvEEETT's second series of experiments (1866), thé ratio of thc oliisticityof form to that of volume is greater thnn that gi~pn by the theory. Ïnbrasa and steel it ia less.–March 7,1867.J ~'MTtf~fT.Tr'ETT TT'