Primary Feathers in Flight. 169 



of one wing (right) were interlocked — the condition of the 

 other wing I had not time to observe." 



" My conclusion, therefore, is that the interlocking of the 

 primaries of the hawks takes place, as Mr Trowbridge has 

 shown, under the conditions of soaring in the face of a strong 

 wind." Written from Rinkai Jikenjo, Misaki-Miura, Japan, 

 September 3, 1905. 



This confirmatory observation of Professor Dean's was 

 apparently made under the most favorable conditions. The 

 observer and the hawk were both moving for a part of the 

 time at nearly the same velocity ; therefore they were approxi- 

 mately stationary with respect to each other, and hence the 

 bird must have appeared almost like a still object and the 

 observation made with certainty. 



The observations presented in this paper have shown that 

 when hawks are killed in certain types of flight a large per- 

 centage of the emarginate primaries of their wings are found 

 interlocked, and it has been proven that these feathers were 

 interlocked for several hours previous to the moment when the 

 hawks were killed ; therefore the principle of the interlocking 

 of the emarginate primaries in flight has been conclusively 

 demonstrated. 



Phoenix Physical Laboratory, Columbia University. 

 New York, September, 1905. 



Am. Jour. Sci. — Fourth Series, Yol. XXI, No. 122. — February, 1906. 

 12 



