570 VITAL ENERGY OF BIRDS. 



with which many of them glide through the path- 

 less air to distant regions, in opposition to the force 

 of gravity. For it is well known, that the hawk 

 and eagle are capable of flying forty-five miles per 

 hour, the carrier pigeon from fifty to sixty, and a 

 species of swallow termed the swift, at the rate 

 of ninety miles per hour, which, if continued for 

 twelve hours, would make 1080 miles a day. And 

 such is the enormous strength of the ostrich, com- 

 bined with rapidity of movement, that if we are 

 to credit the account of Adanson, as reported by 

 Mason Good, it has been known to out-run the 

 swiftest race-horse, with a burden equal to its own 

 weight upon its back. (Book of Nature, vol. i. 

 325.) 



So great is the power of digestion in birds, that 

 common fowls require 2-|- ounces of solid barley 

 per day, as proved by the experiments of 

 Moubray ; or about -^ of their whole weight, 

 supposing the latter to average three pounds. 

 But there is reason to believe, that the smaller 

 and more active species of birds consume a much 

 larger proportion of oxygen than fowls, geese, 

 turkeys, ducks, and other large birds, especially 

 such as are confined to the surface of the earth. 

 For if it be true, as stated by Lavoisier, that two 

 sparrows generate and expire more carbonic acid 

 in a given time than a young guinea pig, they 

 must consume three times the ratio of oxygen ; as 

 the average weight of sparrows is about one ounce, 



