Remarks on Mr. Moon's Papers. 145 



of so great an analyst, is surely no slight recommendation of 

 the theory. 



Mr. Moon subsequently gives a quotation from Airy's 

 Tracts, concerning which he is by no means sparing in arro- 

 gant and supercilious criticism. But is it likely that Airy 

 would make such a fool of himself as Mr. Moon earnestly en- 

 deavours to represent? It must be remembered, that at the 

 lime Airy's Tracts were published, very little of the undula- 

 tory theory was studied or known in Cambridge. 



It was the part of this philosopher, therefore, to put every- 

 thing as much as possible in the clearest and most simple point 

 of view. That there are, and will perhaps long continue to 

 be, difficulties in the undulatory theory, none of its supporters 

 will deny. None of those difficulties are shirked or glossed 

 over in the Tract of Airy ; he plainly acknowledges each as it 

 arrives. He no doubt himself considered the part quoted by 

 Mr. Moon more as an illustration than anything else. Those 

 who wish to see the matter treated with all the analytical ge- 

 nerality of which it is capable, are referred to a tract on the 

 Reflexion and Refraction of Light at the Surface of two con- 

 tiguous Media, by the late famous George Green, in the 

 Cambridge Philosophical Transactions. 



I have one word more with Mr. Moon. He says, that on 

 substituting for u, 



du , d 2 u IP 



and for u', 



dx h + ^ 2 1.2' &C '' 



du 7 d*u h* a 



that h is considered small with respect to u. 



Does Mr. Moon know anything of analysis? He was 

 eighth wrangler in 1838, and therefore he ought to know 

 something. His knowledge, however, has served him mise- 

 rably on this occasion. The substitutions, stopping at h% 

 merely require that h should be small in comparison with the 

 length of a wave, not with respect to u. 



Jesuiticus. 



XXVII. Observations on the subject of the Preceding Com- 

 munications. By the Editors. 



/"^N the subject of the foregoing letter, the Editors are induced to 

 VJ subjoin a few remarks, as besides the attacks on Fresnel, they 

 have also received from Mr. Moon one more paper, containing stric- 



