114 THE FLIGHT OF BIRDS 



or to be facing a head-wind, he may in reality have 

 the velocity of a tail-wind added to his own. We 

 know as a fact that migrant birds do fly at a very 

 great altitude. In 1880 an American ornithologist, 

 Mr. E. D. Scott, at Princetown, New Jersey, used 

 an astronomical telescope to watch birds passing 

 over the disc of the moon at night. To be in focus 

 a bird must be not less than a mile distant ; it was 

 assumed that he would not fly at a greater altitude 

 than 10,000 feet. Knowing the angle made by the 

 telescope with the horizon, Mr. Scott was able to 

 calculate the lower limit ; the birds were flying at a 

 height of not less than half a mile.* 



Another observer, Mr. F. M. Chapman,f also in 

 New Jersey, made a similar use of an astronomical 

 telescope for ornithological purposes, and watched 

 262 birds crossing the face of the moon. Of these 

 233 were calculated to be flying at a height of not 

 less than 1,500 feet. It is remarkable that those 

 that were at a low level were flying upward, as if they 

 had not yet reached the stratum of air most favour- 

 able to flight. Some of the birds, as they passed 

 over the moon's face, were silhouetted so clearly that 

 Mr. Chapman felt confident that he succeeded in 

 identifying the species. 



Mr. F. W. Carpenter, in 1905, J tried a much more 

 elaborate plan. Two telescopes, set at some distance 

 apart — different distances were tried varying from 

 ten to twenty-one feet — were directed upon the moon 

 during a night in May and again during an October 



* Bulletin of Nuttall Ornithological Club, Vol. vi. 

 t The Auk, 1888, pp. 37-39. 

 % See The Auk, April, 1906. 



