260 Mr. William Sutherland on the 



We have to replace our relation 



a varies as Ap*m* 

 by the less accurate one, 



5 1 



a varies as Ap^nv*. 



Multiplying by (Mvf or (M/pf, we get the a(Mo) 1 of 

 Eotvos proportional at all temperatures to AMp ; and as 



d («(Mv) J ) dT is constant, and has been shown by Eotvos to be 

 constant almost right up to the critical temperature, and to be the 

 same for all bodies, we ought, if our assumptions were rigorous, 

 to have AMdp/dT constant almost up to the critical tempe- 

 rature and the same for all bodies (whence another approximate 

 method of finding A or I). Now dp/dT has been shown by 

 Mendeleeff to be constant for many substances within ordinary 

 temperature-ranges ; but the constancy does not hold up to 

 the critical temperature, and the ultimate meaning of the 

 apparent contradiction between Eotvos' s result and this is 

 that, while for most purposes we may safely enough assume 

 p proportional to p, we cannot so accurately proceed to the 



consequence dp^/dT proportional to dp^/dT ; in fact, a change 

 of temperature being accompanied by a change of stress in 

 the surface-layer, the change of p with temperature is more 

 complex than that of p. But within the range of temperature 

 for which dp/dT is approximately constant, we have the 

 important result that 



dT M \ i+ B -V-/3J 

 is constant and is approximately the same for all bodies. 



As I now consider the term differentiated to be not two 

 thirds of the translatory kinetic energy of the gramme- 

 molecule, but two thirds of the sum of the total kinetic energy 

 and the chemic virial, I must replace the verbal statement of 

 the last result as given in my paper (Phil. Mag. April 1889, 

 p. 312) by the following : — The temperature-rate of variation 

 of the sum of the total kinetic energy and the chemic virial 

 of a molecule, measured at low constant pressure, is the same 

 for all bodies (approximately). 



10. Tabulation of Values of the Virial Constant, determined 

 bv four of the five methods described, and multiplied by the 

 square of the molecular weight. — In the first place, I will 

 give a comparison of the values of MH for those bodies to 

 which existing data allow the application of three or four of 

 the previously described methods. The multiplication by M 2 

 is for future convenience. The values obtained by the second 





