CHAPTER IV. 



COURIERS OF THE AIR. 



THE power of flight being almost exclusively the 

 characteristic attribute of birds, it is somewhat 

 strange that even the most eminent naturalists 

 should be silent upon it. And yet this is almost 

 universally so. Those who mention the speed of 

 flight do so upon the most insufficient evidence, as 

 witness Michelet's statement that the swallow flies 

 at the rate of eighty leagues an hour. Roughly 

 this gives us a thousand miles in four hours; 

 but assuredly, even in its dashes, the swallow 

 does not attain to anything like this speed. The 

 Duke of Argyll is rather under than over the 

 mark when he computes the speed at more than 

 a hundred miles an hour. Here, however, the 

 mechanism of flight in the swallows is carried 

 through an ascending scale, until in the swift it 

 reaches its highest degree of power both in en- 

 durance and facility of evolution. Although there 

 are birds which may, and probably do, attain to 

 a speed of one hundred and fifty miles an hour. 



