218 Mr. Earnshaw on Dispersion) in reply to Prof. Powell. 



that mode of argument than for fair philosophical discussion. 

 I am willing to pay my humble tribute to the merits of the 

 two eminent philosophers quoted; but the matter in dispute 

 between Professor Powell and myself lying entirely within the 

 limits of my own reading and understanding, it is not likely 

 that I shall be convinced by any other than a fair appeal to 

 philosophical argument. 



With respect to the Professor's third argument, it appears 

 to me to assume too much. It ought to have been shown 

 that theory has done more for the series (upon which the cal- 

 culations are founded) than merely to indicate that it must 

 proceed according to inverse powers of A ; for if it has, not 

 done more than this, it has in effect done nothing. But even 

 granting that there is something meritorious in the form of 

 the suggested series, I would beg the Professor's attention 

 to two of my objections which still remain in force; — 1st, 

 that the mode of applying it to calculation disconnects it from 

 theory, by rendering the method one of ordinary interpola- 

 tion : and 2ndly, that the results obtained do not coincide 

 sufficiently with experiment to warrant us in concluding from 

 them that the form of the series furnished by theory is the 

 correct one. 



Before I conclude it is necessary to advert to two other 

 matters : the Professor seems to consider that I have used 

 him unfairly in not distinguishing between " certain earlier 

 researches " and those contained in his " published volume." 

 If the Professor will turn again to my letter (p. 309) he will 

 there read that the errors of which I had been speaking, are 

 charged only upon " the first applications of the method." 

 I trust therefore he will be satisfied that I am not guilty of 

 the unfairness of which he complains, and have not committed 

 those " remarkable oversights " of which he (somewhat un- 

 fairly I think) accuses me. And with respect to his having 

 discarded his earliest researches, — " the simple circumstance 

 which renders all my elaborate criticisms superfluous," — I 

 do not regard it as being by any means so fatal to my letter 

 as the Professor seems to think it is : for if he will do me 

 the favour to refer to my letter again he will find that the 

 first part only was directed against the " superseded re- 

 searches," the second part he will find summed up in these 

 words : " the methods of computation employed in compiling 

 the tables contained in the book referred to are wholly un- 

 connected with a physical theory of dispersion, and therefore 

 were they even coincident with experiment add nothing to the 

 strength of M. Cauchy's theory ; and were they even more dis- 

 cordant than they are with experiment, tend in no degree to 



