316 Prof. Liveing, On the measurement of kinetic [Oct. 26, 



The following were elected Associates : 



Mr Eobt. Bowes. Mr W. Marshall. 



Mr J. Carter. Mr H. Middleton. 



Mr A. Deck. Mr W. E. Pain. 



Capt. P. Going. Mr W. W. Smith. 



Mr W. Heape. Mr K. H. Solly. 

 Mr R. T. Lynch. 



The following communications were made to the Society : 



On the measurement of kinetic molecular energy on an absolute 

 scale. By G. D. Liveing, M.A., F.RS. 



In treatises on thermo-dynamics no definition is usually given 

 of the particular molecular motions which are to be regarded as 

 heat. At least two very different kinds of motion are included 

 under the name heat by all writers on the subject, namely the 

 motion in a gas which produces pressure and the motion which 

 produces radiation. Most writers now-a-day distinguish between 

 heat and the motions of liquefaction, vaporization, and that of 

 decomposition of molecules, and such expressions as "latent heat 

 of evaporation" are used under protest, or changes of state are 

 reckoned as internal work. When heat is employed to do ex- 

 ternal work it is almost exclusively the motion of translation 

 of the molecules of gases which is directly employed, but the 

 energy is supplied to the working substance by conduction in the 

 form of heat, and all the other forms of energy that I have men- 

 tioned may be drawn upon, even the energy of dissociated chemical 

 elements if there are such in the supply. For the sake of dis- 

 tinctness in what follows I shall use the word " heat " to mean 

 only those forms of energy which consist in the vibratory motions 

 producing radiation and those w T hich pass in conduction. I do 

 not pretend to say that these two kinds of motion are identical, 

 but merely that for the present I class them together as one form 

 of energy which all, so far as I know, call " heat." The motions 

 of liquefaction, vaporization, and of the breaking up of molecules 

 into simpler parts I shall distinguish from heat as separate 

 forms of kinetic molecular energy. Nevertheless when the supply 

 from which heat is drawn to work an engine consists of any 

 ordinary materials in a state of thermal equilibrium at first, then 

 when heat is withdrawn from them an adjustment takes place 

 between all the forms of kinetic molecular energy in the supply 

 in accordance with the law of dissipation whereby, in general, 

 they all ultimately contribute their quotas to make good in part 



