154 



Trowbridge — In terlocking of Em arginati 



In the case of Series 4 and 8 a photographic method was 

 employed and the width of the notches measured by means of 

 a Repsold star plate measuring machine loaned for the pur- 

 pose by the Department of Astronomy, Columbia University. 

 The caliper method was used in subsequent measurements 

 because it was found to be sufficiently accurate. 



The' method of photographing the primaries consisted in 

 constructing a standard S, as shown in fig. 8, to support both 

 camera C and the primaries P. The latter were held in posi- 

 tion by thumb-tacks T. An auxiliary lens, L, was used by 

 wdiich a life-sized image was formed on the film when the 

 object was held on the standard, 15 centimeters from the lens. 



Photographs of the notches in the first primary feathers are 

 shown in figs. 9 and 10. The former is one of the photographs 

 of Series 1, a Sharp-shinned hawk. The latter is one of Series 



^^^^^ 



8, an Osprey, which was moulting and the primary had not 

 completed its growth ; therefore, the notch is not at the point 

 where the emargination begins, which is the usual case. The 

 photographs given were selected from among those in Series 4 

 and 8 as giving the best definition for reproduction. 



Curves have been drawn from the measurements showing 

 the recovery of the web of the feathers after the pressure 

 caused by the interlocking of the feathers was relieved. Sim- 



