114 MOLECULAR MOTION AND ITS ENERGY 50 



their condensing point, but also the fact that their volume- 

 and pressure-coefficients are greater than those of ideal 

 gases. 



51. Claims of the Two Explanations 



In the present position of the matter a definite answer 

 to the question, Which of the two explanations of the anoma- 

 lies deserves preference ? is not possible, since each represents 

 the observed behaviour in general, and neither seems to con- 

 tradict our gaseous theory, which is otherwise confirmed. A 

 distinction between them could only be made after a further 

 pursuit into details of the views that have only been 

 sketched very generally. 



In order to carry out the theory of gases with the sug- 

 gested corrections in the one direction or the other, the 

 calculus of probabilities offers the same method as was 

 used to prove Maxwell's law of speeds. It would be only 

 necessary to consider as unknown not only this -law of dis- 

 tribution, but also the form of combination of the molecules, 

 whether in groups or as units. The problem offers the same 

 difficulties as a mathematically formulated chemical statics, 

 which would have to treat of the combination of atoms into 

 molecular groups ; and the solution of the one will be the 

 solution of the other. 



The contention between the two modes of explanation 

 seems to be capable of more easy decision empirically. It 

 might be recommended to determine the densities of vapours 

 not only by weighing, but also indirectly in the way proposed 

 by Leslie and Bun sen, viz. by observation of their speeds 

 of effusion at different temperatures and under different 

 pressures. Perhaps, too, transpiration- and thermal-measure- 

 ments may give help in the determination. 



At present we shall look on both explanations as equally 

 entitled to consideration, and must consider the probability 

 to be that both circumstances, as discussed in 48-50, work 

 together to cause actual gases and vapours to deviate in 

 their behaviour from the ideal laws. 



