On the Kinetic Energy of the Motion of Heat. 501 



ana\reduced to the nitrogen thermometer of the Bureau Inter- 

 national des Poids et Mesures is to the nearest unit 775 foot- 

 pounds at the sea-level and the latitude of Greenwich. The 

 number refers to a pound of water weighed in vacuo at a 

 temperature of 61°-7 F. (16°'5 C.) . 



The equivalent reduced to ergs becomes 4*173 X 10 -7 . 



It is not necessary to discuss the older observations of Joule, 

 or to modify his numbers by attaching weights to his experi- 

 ments different from those which he gave to them himself. 

 The result of Joule's last paper, as reduced by himself, should 

 be taken as his final judgment. Rowland's value at 16 0, 5 is 

 4' 186 x 10 7 , but the results of this paper open out the pos- 

 sibility that this number might have to be reduced somewhat 

 when referred to the Paris air-thermometer. It seems most 

 probable that the correct value of the equivalent lies some- 

 where between Joule's value and that of Rowland. The higher 

 values obtained by Mr. Griffiths and myself and Gannon by 

 the electrical method are not easily accounted for, but for the 

 present they cannot in my opinion be put into competition with 

 the direct determinations of Joule and Rowland. The dis- 

 crepancy no doubt will be cleared up. In the meantime 

 a comparison between one of Rowland's thermometers and 

 the Paris standard would be of great interest. 



XL IX. On the Kinetic Energy of the Motion of Heat and 

 the corresponding Dissipation Function. By Dr. Ladislas 

 JSTatanson, Professor of Natural Philosophy, University of 

 Cracow*. 



1. TN the following the fundamental assumptions of the 

 JL former paper (" On the Kinetic Interpretation of the 

 Dissipation Function ") will be adopted. A fluid medium is 

 considered which is supposed to consist of a multitude of 

 moving molecules. Let it, v, w be the components of the 

 " molar " velocity, i. e. of the mean velocity of the molecules 

 within an element dx dy dz ; and let £, 77, f be the components 

 of the individual velocity of any given molecule in that 

 element. We will employ the symbol p to denote the density 

 of the medium ; and Q to denote any property of a molecule 

 which depends on the values of (w + jf), (v + tj), and (w + £). 

 Let Q indicate the mean value of Q for all molecules within 



* Translated from " Rozprawy " (Transactions) of the Cracow Academy 

 of Sciences, Math, and Phys. Section, vol. xxvii. Communicated by the 

 Author, 



