292 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 2 



the action of the wing, will slide out sideways/" or even move upwards 

 over the wing tip into the region of reduced pressure to join forces 

 with another stream of air that is doing no good. This other stream 



COMMON rER\ Bl«CK-HL»Oq> SWALLOW COLDENPlOVtR WOODCOCK SHORT-tAP.ED CRtAT CRE5TED 



^ttrnahirunao Gull HirurJao rust'ca Cf>arjar,ui Sco/o/>^x OWL CREBE 



RUODV NIGHT-HtRON WRYNECK 



<MEID-D11CK /l/yct/ecrBX /ynz rorfuilla 



Cfisa^-co nycCieorax * 



ferrvgt/iH> 



STARLING 



SCur/ju$ vut^ans 



SKV-LARK 



Alauda 



eOlOFINCH SONC-THRUSH BLACKBIRD 



BUZZARD HOOPOE 



RED - LEGGED 

 PARTRIDGE 



FiGDUE 28. — Wings of a number of representative types of birds in fully- 

 spread position. All are reduced to a common size for the sake of 

 comparison 



consists of air that is moving in sideways to assist in filling up the 

 partial vacuum on the top of the wing. 



1* The reason in technical language is that a gas which is compressed will tend to ex- 

 pand equally in all directions. By the same token it will tend to flow into a space where 

 there is a reduced pressure; that applies to the top of the wing. 



