256 M. C. Szily on the Dynamical Signification of the 



of thermic quantities are inadequate, and, taken strictly, are 

 not even correct. It became evident that, before all, these con- 

 ceptions must be sifted, and, indeed, in part generalized, in 

 part rendered more precise. I now resolved to give up many 

 of the usual ideas, and to substitute for them more general 

 and, in my opinion, more precise notions. Arrived at this 

 point, the deduction was immediately found to be more simple, 

 more natural. 



I now make public the results which I have hitherto at- 

 tained, viz. (1) the necessary modification of the notions in 

 the theory of heat, (2) the dynamic deduction of the Second 

 Proposition carried out on the basis of the altered notions, 

 (3) conclusions resulting from the new conception. 



One of the first things assumed in the mathematical treat- 

 ment of the theory of heat is that the thermal state of a body 

 is constant so long as its volume and temperature remain un- 

 changed. Since in this is given merely a one-sided, and 

 moreover a rather loose definition of that unknown something 

 which is usually named " constant state," taken as it stands we 

 can offer no objection to it. It has, however, been customary 

 to add that it is only when the volume and temperature of a 

 body remain continuously constant that its thermal state can 

 and ought to be regarded as unchanged, and that, with any 

 (even an infinitesimal) change of the volume or the tempera- 

 ture, a corresponding alteration of the thermal state ensues. 

 But is this correct ? If we adhere to this definition of constant 

 state absolutely, can we presume that there exist bodies the 

 state of which can in this sense be regarded as invariable ? 

 For my part, I believe that there does not exist in nature a 

 body of which it could be assumed that its state, thus defined, 

 remains constant, even during only an infinitesimal space of 

 time. 



For every body can be considered as an aggregate of num- 

 berless, but not infinitely many, material points in continual 

 motion, under the influence of external and internal forces, 

 according to certain unknown laws. Let us picture to our- 

 selves a body with its numberless molecules and the pro- 

 portionally large interspaces between them. Let us contem- 

 plate this little world at a certain instant, 2 = 0. Each mole- 

 cule has at this instant a certain position, a definite velocity 

 and acceleration; and it may happen also that the velocity 

 of many a one is just zero. And now let an indefinitely short 

 time dt pass, after the lapse of which we will contemplate the 

 body again. We perceive an entirely changed constella- 



