of the Newtonian Law of Molecular Action. 443 



wave's front." By this process it is established beyond the 

 possibility of a doubt, that when the operation represented by 

 £ is performed in the expression which Professor Kelland 

 quotes (p. 268) from M. Cauchy, the result ought to be in- 

 dependent of the position of the wave's front ; and so it is 

 proved either that my equations and M. Cauchy's are identical, 

 or that M. Cauchy's are at variance with experiment. The 

 methods by which we have obtained our equations are perfectly 

 dissimilar, but I believe the equations themselves are identical. 

 In deducing his M. Cauchy has adhered closely to theoretical 

 considerations ; but in deducing mine, I have proceeded to a 

 certain point by the guidance of theory, and then beginning 

 from a more advanced point, where the results of experiment 

 were known, have worked backwards to meet theory. It is 

 therefore easily seen that my results being a mixture of theory 

 and experiment would not present the same appearance to the 

 eye as the results of M. Cauchy, which are obtained from 

 theory alone. They must, however, be identical in fact, or 

 else theory is discordant with experiment. What therefore 

 Professor Kelland has written (p. 268) about " the axis of 

 transmission" is grounded on a misconception, from which 

 also has sprung his idea that " the form of my equations " 

 (p. 46), from which my inferences have been drawn against the 

 Newtonian law, &c, " does depend on the position of the front 

 of the wave." 



I believe I have now replied to every objection of import- 

 ance which Professor Kelland has brought forward ; I cannot 

 however conclude this letter without remarking, that it is ob- 

 vious that a discussion like the one in which we are now en- 

 gaged never can be brought to a satisfactory conclusion un- 

 less both parties write with perfect candour and a single eye to 

 the discovery of the truth. All arguments which do not really 

 bear upon the Newtonian law must be avoided ; and those 

 which do bear upon it, if after due scrutiny they be found to 

 be true, unhesitatingly admitted with all their consequences. 

 I would therefore, with a view of shortening our labours, re- 

 spectfully request the Professor not to take so wide a field, 

 but to confine himself to the prominent and really important 

 points of the argument ; because if objections of this character 

 cannot be answered, it is clearly quite unnecessary for him to 

 descend with M. Cauchy into the mystical and doubtful sub- 

 tilties of "refined analysis." May I then respectfully re- 

 quest the Professor to answer in the spirit here recommended 

 the four following queries, which seem to me better calculated 

 than any others to bring our discussion to a speedy termina- 

 tion? — 



