HERBERT SPENCER 25 



sometimes play on his flute. On remarking to him one day 

 that I wondered he could live among such unintellectual 

 people, he said that he had purposely chosen such a home in 

 order to avoid the mental excitement of too much interesting 

 conversation; that he suffered greatly from insomnia, and 

 that he found that when his evenings were spent in common- 

 place conversation, hearing the news of the day or taking 

 part in a little music, he had a better chance of sleeping. 



In the autumn of 1867 I read the Duke of Argyll's " Reign 

 of Law," and though I found much that was erroneous and 

 weak in argument, I thought his discussion of the mode of 

 flight in birds, founded largely on personal observation, was 

 very good; in fact, the best I had seen. Spencer had also 

 read this, and differed from me, thinking that important parts 

 of the duke's theory of flight were not true, because they would 

 not apply equally to bats ; and we had quite a discussion on the 

 subject. The next day, after thinking the matter over, I 

 wrote him a long letter of eight pages, trying to show that the 

 general principles of flight in birds, bats, and insects were the 

 same; but that in birds there were additional special adapta- 

 tions that render their flight more perfect, and their power of 

 motion through the air, under adverse conditions, more varied 

 and more complete. The duke, dealing with birds only, had 

 dwelt most on these special adaptations (chiefly, if I remem- 

 ber, the beautiful overlapping and movements of the separate 

 feathers increasing resistance during the downward, and de- 

 creasing it during the upward stroke) which did not exist in 

 bats or in insects. I also showed that although this adaptation 

 was absent in the wings of insects, the general form and move- 

 ments of the wings were similar and produced similar, but not 

 identical results. In his reply he admitted the accuracy of my 

 description of the flight of insects, but made the following 

 remark in furtherance of his former objection as regards the 

 duke's account of the flight of birds : " If you will move 

 an outstretched wing backwards and forwards with equal 

 velocity, I think you will find that the difference of re- 

 sistance is nothing like commensurate with the difference 

 of size between the muscles that raise the wings and the 



