THE HEIGHT AND SPEED OF PLIGHT 49 



that the small birds noticed would average 6 inches 

 in length, calculated a height of 2000 feet above sea- 

 level. At Detroit, Winkenwerde obtained estimates 

 of a little over half a mile, and R. A. Bray, in Eng- 

 land, saw birds crossing the sun in September 1894 

 which were invisible to the naked eye and must 

 have been 2 or 3 miles away (11). 



In December 1896 Mr H. H. Clayton, at Blue Hill 

 Observatory, saw ducks flying at a height of 958 feet. 

 He was at the time engaged in measuring the height 

 and velocity of clouds, and was able to estimate the 

 speed of the birds at nearly 48 miles per hour. In 

 March geese passed at over 900 feet at 44.3 miles 

 per hour. In 1905 Prof. Stebbins and Mr Carpenter 

 worked out a scheme for ascertaining heights by 

 simultaneous observation from different points. 

 They based their calculations only on birds which 

 were observed by them both, and found that these 

 passed at various altitudes, ranging from 1200 to 

 2300 feet ; in the following October the lowest alti- 

 tude observed was 1400 feet, and the highest 5400. 

 Allowing the 25 per cent possible error, these results 

 are of great value. 



Mr Chapman's remarks about the upward flight 

 of some of the birds are enlightening, for when birds 

 start on oversea journeys they frequently ascend to 

 a great height. Dr Allen and others think that the 

 ascent is to increase the visible distance, but it may 



