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UKPoiiT — 1884. 



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US nocordini,' to Bosrovicli, fiidowed with forces of iiiut mil po.sitive ami ncjjiitivi' 

 iittriictiini, varyiiij^ uccordii)); (<> sdtiii' definite fuiictiim nl' the ilistniici', \vc i iuirmi 

 avoid tlio qiie.-ition f)f iniiiiicts, ami of viiiiatioiix ami mtalions of tlie inolt-ciilcs 

 resultin<.' from iinnacts, and we must look <listinctly on lacli molecule as bciiii.' 

 (iitlier a little eliustic solid, or a conli>ruration of motion in u continuous all-]terviid- 

 ing liquid. I do not myself see liow we can evi-r pernnineiitly rest any when- slimt 

 of this last view ; hut it would ho a very pleasant temi)ornry restin},'-]iliice on tin' 

 way to it, if we could, as it were, nuike a mechanical mo(|il of a pis out of litilr 

 pieces of round perfectly elastic solid matter, llyiii;;' nI)out thronjih the spiicn 

 occupied by the <,'as, and collidiii};^ with one another iiiid ajrainst the side* of tln' 

 containing vessel. This i.s, in fact, all wc- have of the kirn tic theory of gasrs n]) to 

 the present time, and this has done for us, in the hands of Chuisius and Maxwell, 

 the {jreat thinj^'.s which constitute our ilrst step towards a molecular tlieory of 

 matter. Of course from it we .should have to po on to tind an explanation of tli" 

 elasticity and all the other properties of the molecules them>elves, a subject vastiv 

 more complex and dillicult than th(> gaseous ))ropertie», for the explanation d' 

 which we assume the elastic; molecule; but without any explanation of tln' pro- 

 perties of the molecule itself, with merely the ft8sumi)tioM thai the molecult' luistln' 

 requisite properties, we might rest happy for awhile in thecoiiiemjilatioii of the kinetic 

 theory of gases, ami its explanation of t lie gaseous jimperties, which is not only 

 KtuiM'iidously important ns a ste]) towards a more tlun'ough-going theory of mutter. 

 but is luulouhtedly the expression of a perfectly intelligililo and definite set of 

 facts in nature. Ihit alas for our mechanical model consi>ting of the cloud of 

 little elastic solids Hying about amongst one another. Though each partich- hiivr 

 absolutely perfect elasticity, the end must be prett)- miicli the same as if it wen- 

 but imperfectly elastic. The average elfect of repeated and rejjeated mutual 

 collisions must ho to gradually convert all the transhitional energy into emvgy of 

 shriUer and .shriller vibrations of the molecule. It .sernis certain tluit each colli.-ioii 

 must have something more of energy in vibrations of very liiiely divided nodal ))art> 

 than there was of energy of such vihrations before the imjiact. The moi'e minute 

 this nodal .subdivision, the lesa must b'^ the tendency to give up part of the 

 vibrational energy into the siaapo of translational energy in the course of a collision, 

 and I think it is rigorously demonstrable that the whole translation.'vl energy must 

 ultimately become transformed into vibrational energy of higher and higher nodal 

 subdivisions if each molecule is a continuous elastic solid, l^et us, then, leave the 

 kinetic theory of ga.se8 for a time with this dilliculty unsolved, in the hope that we 

 or others after us may return to it, armed with more knowledge of the properties 

 of matter, and with .sharper mathematical weapons lo cut through the harrier 

 which at present hides from us any view of the molecule itself, and of the elfecis 

 other than mere change of transhitional motion which it experiences in collision. 

 To explain the elasticity of a gas was the primary object of the kinetic theory 

 of gases. This ol)jeet is only attainable by the assumption of an elasticity more 

 complex in character, and more dillicult of explanation, than the elasticity oi' 

 ga.Hcs — the elasticity of a solid. Thus, even if th»^ fatal fault in the theory, to whidi 

 1 have alluded, did not exist, and if we could be perfectly satisiieil with the 

 kinetic theory of gases founded on the collisions of elastic .solid molecules, there 

 would still be beyond it a grander theory which need not he considered a chimericid 

 object of scientific ambition — to explain the ela.sticity of solids, lint we may he 

 .stopped when we commence to look in the direction of .such a theory with the 

 ♦•ynical question: What do. you mean by explaining a property of matter i*' As 

 to being stopped Oy any such question, all 1 can say is that if engineering were 

 to be all and to end all physical science, we should perforce be content with merely 

 tinding properties of matter by observation, and using them for practical purpcses. 

 IJut 1 am sure very few, if any, engineers are practically satisfied with so narrow 

 a view of their noble profession. They must and do patiently observe, and dis- 

 cover by observation, properties of matter, and results of material corabinations. 

 JJut deeper questions are always present, and always fraught with interest to the 

 true engineer, and he will be the last to give weiglit to any other objection to any 

 attempt to see below the surface of things than the practical question: Is it likely 



