114 THE FLIGHT OF BIRDS 
or to be facing a head-ygnd, 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, 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. v1. 
+ The Auk, 1888, pp. 37-39. 
t See The Auk, April, 1906. 
