Page:The Migration of Birds - Thomas A Coward - 1912.pdf/64

48 Most of these observations were at first made by accident; birds were seen through astronomical telescopes passing acres»; the face of the moon or sun; but recently this method of observation and several ingenious plans of measuring height and speed have been made use of expressly to study migration. W. E. D. Scott, at Princetown in 1880, thought that by shape and size he could even recognise two species, Chrysomitris tristrisChrysomitris tristis [sic] and Quiscalus purpureus, which passed across his field of vision at a height of at least half a mile above the earth (43). In 1888 Mr Frank M. Chapman published an account of similar observations; he calculated that the birds passed at distances varying from one to five miles, and that their altitudes must therefore have been between 600 to 1000 feet: and 3000 to 15,000 feet. He adds an important note: "A number of birds were seen flying upwards, crossing the moon, therefore, diagonally, these evidently being birds which had arisen in our immediate neighbourhood, and were seeking the proper elevation at which to continue their flight," but the direction of flight of most of the birds which were observed was parallel to the earth's surface and southerly. The average height was certainly far above the inferior limit (13).

Mr F. W. Carpenter, reviewing these astronomical calculations, that Verey compared the apparent size of birds with lunar features, and considering