Correspondence on Biology, etc. 



microscopic examination of both these means of transport. — 

 Believe me ever truly yours, Cha. Lyell. 



Sib C. Lyell to A. E. Wallace 



73 Harley Street. July 3, 1867. 



My dear Mr. Wallace, — I was very glad, though I take in 

 the Westminster Review, to have a duplicate of your most 

 entertaining and instructive essay on Mimicry of Colours, 

 etc., which I have been reading with great delight, and I may 

 say that both copies are in full use here. I think it is admir- 

 ably written and most persuasive. — Believe me ever most 

 truly yours, Cha. Lyell. 



To Herbert Spencer 



Hurstpier point, Sussex. October 26, 1867. 



My dear Mr. Spencer, — After leaving you yesterday I 

 thought a little over your objections to the Duke of Argyll's 

 theory of flight on the ground that it does not apply to 

 insects, and it seems to me that exactly the same general 

 principles do apply to insects as to birds. I read over the 

 Duke's book without paying special attention to that part 

 of it, but as far as I remember, the case of insects offers no 

 difficulty in the way of applying his principles. If any wing 

 were a rigid plane surface, it appears to me that there are 

 only two ways in which it could be made to produce flight. 

 Firstly, on the principle that the resistance in a fluid, and I 

 believe also in air, increases in a greater ratio than the 

 velocity (? as the square), the descending stroke might be 

 more rapid than the ascending one, and the resultant would 

 be an upward or forward motion. Secondly, some kind of 

 furling or feathering by a rotatory motion of the wing might 

 take place on raising the wings. I think, however, it is clear 

 that neither of these actions occurs during the flight of 



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