V ° 1 1906 111 ] Carpenter, Height of Migrating Birds. 211 



showing the probable limits of height between which the birds 

 were flying. In so doing it was necessary to assume that the least 

 distance from the observer at which birds could be seen was one 

 mile, and the greatest distance five miles. The computation of 

 the heights showed that the birds were flying between six hundred 

 and fifteen thousand feet; and since it was evident that "the 

 major portion passed at what may be termed the middle distance" 

 the average height was apparently far above the inferior limit. 

 To both observers a nearer approach to an accurate measurement 

 of the altitude did not appear possible. Mr. Chapman wrote: 

 "The problem of determining this height exactly is not, so far as 

 we can now judge, capable of a definitive solution, for the reason 

 that we have no means of ascertaining the distance of the bird from 

 the observer." 



The foregoing observations have been accepted by J. A. Allen, 1 

 Newton and Gadow 2 and other ornithologists as fair evidence 

 that migrating birds fly at night at very considerable altitudes, 

 and comment has often been made on the favorable position in 

 which birds are thus placed for observing the prominent features 

 of the landscape which may serve to guide them on their way. 

 As an example of an extreme view in this connection it should be 

 recalled that Giitke in his book entitled 'Die Vogelwarte Helgo- 

 land' gives his reasons for supposing that an altitude of thirty 

 thousand feet or even more may be attained. 



More recent attempts to measure the altitude of the migratory 

 flight have indicated that this has been over-estimated. The 

 methods used have, however, like former ones, involved apparently 

 unavoidable assumptions, which, though probable, do not admit 

 of strict verification. 



The heights of migrating birds seen against the moon in Sep- 

 tember, 1896, at the Ladd Observatory, Providence, Rhode Island, 

 were calculated by F. W. Very, 3 who compared the apparent size 



1 Notes appended to the articles by W. E. D. Scott cited above. Also review 

 of Gatke's 'Heligoland.' Auk, 1896, Vol. XIII, No. 2, pp. 137-153. 



2 Newton, A., and Gadow, H., '93-96. A Dictionary of Birds. London, xii + 

 1088 pp. 



3 Very", F. W., '97. Observations of the Passage of Migrating Birds across the 

 Lunar Disk on the Nights of September 23 and 24, 1896. Science, N. S., Vol. VI, 

 No. 141, pp. 409-411. 



