SAFETY DEVICES IN WINGS OF BIEDS ' 



By Lieut. Commander R. 11. Graham, R. N. 



GLOSSARY OF TERMS USED 



AiK Stream. — The flow of air felt by a bird or any part of a bird owing to its 



motion through the air. 

 Aib-Stkeam Gradient. — The upward or downward shjpe of the air stream felt 



by a point on the wing of a bird in flapping flight, the angle of slope 



depending upon the proportion of vertical speed at that point to horizontal 



speed of flight. 

 Aspect Ratio. — The proportion of lengtli to breadth of a wing. Obtained in 



figures by dividing the length by the mean breadth. 

 Babbicels. — Of a feather ; the miscroscopic branches that spring from some of 



the barbules. Some are simple spines, others are hoolied. 

 Barbs (or Rami). — Of a feather; the branches that spring at an angle from 



the shaft, and, in mass, form the webs. 

 Babbules (or Radh). — Of a feather; the minute branches that spring from 



the barbs. Some are branched, others not. 

 Blade. — Of a wing or feather ; the whole surface ; i. e., of a feather, the two 



webs considered together. 

 Camber. — The curve of a wing between the leading and trailing edges. 

 Cord. — Of a wing or feather ; the distance between the front and rear edges 



when in flying position. 

 Covert Feathers. — The small feathers of a wing which cover up the gaps 



between the shafts of the flight feathers near their roots wliere they are 



devoid of barbs. 

 Cutting Edge. — Of a feather ; a stiff, narrow form of front web, designed to cut 



the air ; that is, to act without the support of another feather in front. 



Found along the whole front web of the first fiight feather in all birds ; but 



in other feathers only wliere their front webs are emargiuated. 

 Emakgination. — Of a feather ; the stepping down in width toward the tip, 



either of one or both webs. Only found in certain primary feathers of 



certain types of birds. 

 Flight Feathers. — The principal feathers of a wing ; i. e., the visible primaries 



and the secondaries. 

 Incidence. — The angle between the blade of a wing or feather and the line 



of the air stream which it encounters at any moment. This angle deter- 

 mines the depth of the furrow a wing cuts in the air. 

 Leading Edge. — The front margin of a wing or feather in flying position. 

 Peimaey Feathers. — The main feathers that spring from the hand of a bird's 



wing. In some birds the first primary is so small that normally it can not 



be seen. The second primary is then considered as being the first flight 



feather. 



1 Reprinted by permission from British Birds, vol. 24, Nos. 1, 2, 3, 1930, and tlie Jour- 

 nal of the Royal Aeronautical Society, vol. 36, No. 253, January, 1932. 



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