THE LIFE OF MATTEK. 407 



K'nu'i'ic conceptual (.)J: moh'ciilar iiKircmcntx. — Tho idea of tliis peculiur 

 ugitation is by no means- ne\V" to us. Wo wore familiarized with it 

 in scientitic theories during our colicgo days. The atomic theory 

 teaches us that matter behaves, from a chemical point of \ imv, as if it 

 were divided into molecules and atoms. The kinetic theory explains 

 the constitution of gases and the effects of heat by supposing that 

 these particles are endowed with movements of rotation and displace- 

 ment. The wave theory explains luminous phenomena by supposing 

 peculiar vibratory movements in a special medium, the ether. But 

 these are merely hypotheses which are not at all necessary; they are 

 the images of things, not the things themselves. 



Reality of the morements of particles. — Here there is no question of 

 Iwpotheses. This intestinal agitation, this interior work, this inces- 

 sant activity of matter are positive facts, an objective reality. It is 

 true that when the chemical or mechanical equilibrium of bodies is 

 disturbed it is restored more or less slowly. Sometimes days and 

 3"ears are required l)efo!e it is regained. Scarcely do they attain this 

 relative repose when they are again disturbed, for the environment 

 itself is not fixed; it suti'ers variations which react in their turn upon 

 the body under consideration; and it is only at the end of these varia- 

 tions, at the end of theii' respective periods, that they together attain, 

 in a universal uniformity, an et(M'nal repose. 



We shall see that metallic alloys undergo contimial physical and 

 chemical changes. They are always seeking an e(|uilil)rium which more 

 or less escapes them. Physicists in modern times have given their atten- 

 tion to this intestinal activity of material })odies in pursuit of stal)ility. 

 Wiedemann, Warburg, Tonilinson. MM. Duguet, Brillouin, Duhem, 

 and Bouasse have revived tiie oldex})erimental studies of C'ouloml) and 

 Wertheim upon the elasticity of bodies, the etiects of ])ressure, traction, 

 hanuiiering of metals, tempcn-ing, and annealing. 



The intestinal actixity manifested under these circumstances pri\sents 

 quite remarka])le characteristics which have been almost necessarily 

 compared to the analogous phenomena presented by living bodies. 

 There has been created, e\ en in physics, a iigurati\e terminology, and 

 metaphorical expressions have been borrowed from biolog\'. 



Conepartsoii of the actirlty (fpartlclcx mit/i tufaJ act ir it//. -It was 

 Lord Kelvin who first spoke of the fatigue of metals, or \\\v fatigue of 

 elasticity, and, since then, Bose showed for these same l)odies the 

 fatigue of the electric touch [tact electricjue]. The term acconnnodation 

 has been employed in the study of torsion, and according to 'I'ondinson, 

 for preciseh' those [)henomeiui which are the inverse of those of fatigue. 

 The phenomena pres(>nted by glass when it is sul)jected to an exterior 

 force which slowly bends it, have Ihmmi considered as thost> of adapta- 

 tion. The m.ethods by which a bar of steel resists wire-drawing ha\'c 

 been legarded as means of defense against threatened rupture. And 



