284 CONTINUOUS VIBRATORY MOVEMENT OF 



bines into small sjiheres the particles of water, has given to all the great celes- 

 tial bodies their spherical form. 



[This statement is scarcely correct in a critical consideration of the phenomena; 

 the spherical form of the planets is due to the attraction of every particle of the 

 whole body on every other, while the spherical form of the globule of oil is the 

 result of the interaction or cohesion of the particles at the surface. — J. H.] 



But, besides imiversal attraction, matter in masses has received, at its origin, 

 movements of translation, and by analogy the molecules of a drop of water or of a 

 globtile of platina — which are as thinly scattered and as rai'C in the little space 

 thej' occupy as the stars of our solar system — may be supposed to be in per- 

 petual oscillatory revolutions, without losing anything of their stability, thanks 

 to the nature of these movemer.ts, and to the influence of the neighboring bodies. 



The astonishing phenomena of acoustics completely forestall the species of 

 repugnance we experience in admitting that the molecules of solids can execute 

 very rapid movements without becoming disaggregated. On seeing the violent 

 movements which pulverulent bodies undergo, and the regular figures they de- 

 scribe when cast on plates of glass, metal, or wood, which are made to render a 

 sound by scraping them with a bow ; on hearing sound propagated through solid 

 bodies more quickly than through the air, and recognizing that it suffices to 

 impress a vibratory movement on a small portion of a rigid body in order to com- 

 municate to a considerable mass a lively agitation ; on verifying that a metallic 

 rod which is made to vibrate longitudinally undergoes contractions and elonga- 

 tions, condensations and dilatations, just as does a column of air which resounds 

 in a tube ; at seeing a thick beam in contact with a vibrating body of small 

 dimensions undergo elongations which may amount to the tenth of a millimetre 

 for a metre of length : in presence of this species of mechanical paradox, accord- 

 ing to which simple external vibrations of so feeble a nature produce such con- 

 siderable effects, we can no longer refuse to admit that the immobility in wdiich 

 we see the molecules of solid bodies is only apparent. 



The recent experiments of Professor Graham, on the diffusion of gases 

 through graphite, confirm the hypothesis which considers gases as masses com- 

 posed of innumerable particles, of atoms spherical, solid, endowed with a perfect 

 elasticity, and moving in all directions, but with variable velocities according 

 to the s})ecial nature of each gas. If the substance of the vessel be porous like 

 that of the diffitsioiiicter, the atoms of the gas, under the influence of the active 

 force which animates them, are j)rojected through the pores of the graphite, real 

 tunnels, as the}^ are in comparison with the minute dimensions of the elementary 

 atoms of the gaseous body, which thus, in the end, escapes and disperses itself 

 in the exterior atmosphere. But, at the same time, the air or some exterior gas 

 enters in like manner into the interior and replaces the gas which issued from it. 

 We may well conceive that this same atomic movement, accelerated by heat and 

 retarded by cold, may be the cause of the elastic force of all gaseous substances 

 and of their reaction against all comjn-essing actions. It is known that no alter- 

 ation in these movements is manifested when the same gas exists at the interior 

 and at the exterior of the vessel, and consequently in contact with both faces of 

 the porous wall. It may be assumed in this case that the gaseous molecules enter 

 and issue exactly in the same proportions, and thus undergo changes of place 

 which we can neither perceive by variations in volume nor by any other phe- 

 nomenon. 



If the gases which are in communication are of different natures, but possess 

 nearly the same density, and are animated by molecular movements of the same 

 velocity, there is again a simple displacement of molecules without auguientation 

 of volume, as experiment has shown in the case of nitrogen and the oxide of 

 carbon, If, on the contrary, the gases separated by the porous wall are of different 

 densitv and molecular velocity, the reciprocal penetration ceases to be equal in 



