AERONAUTICS. 



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front, and a flexiUe sail (a, 6) composed of feathers, behind. It 

 acts upon the air, and the air acts upon it, as occasion demands. 



Chabrier's Fi"^^^;^.— Chabrier states that the wing has only 

 one period of activity — that, in fact, if the wing be suddenly 

 lowered by the depressor muscles, it is elevated solely by the 

 reaction of the air. There is one unanswerable objection to 

 this theory — the bats and birds, and some, if not all the 

 insects, have distinct elevator muscles. The presence of well- 

 developed elevator muscles implies an elevating function, and, 

 besides, we know that the insect, bat, and bird can elevate 

 their wings when they are not flying, and when, consequently, 

 no reaction of the air is induced. 



Straus-Durckheiw! s Views, — Durckheim believes the insect 

 abstracts from the air by means of the inclined plane a com- 

 ponent force (composant) which it employs to support and 

 direct itself. In his Theology of Nature he describes a sche- 

 matic wing as follows : — It consists of a rigid ribbing in front, 

 and a flexible sail behind. A membrane so constructed will, 

 according to him, be fit for flight. It will suffice if such a 

 sail elevates and lowers itself successively. It will, of its own 

 accord, dispose itself as an inclined plane, and receiving 

 obliquely tJie reaction of the air, it transfers into tractile force a 

 part of the vertical impulsion it has received. These two parts 

 of the wing are, moreover, equally indispensable to each other. 

 If we compare the schematic wing of Durckheim with that of 

 Borelli they will be found to be identical, both as regards 

 their construction and the manner of their application. 



Professor Marey, so late as 1869, repeats the arguments 

 and views of Borelli and Durckheim, with very trifling altera- 

 tions. Marey describes two artificial wings, the one composed 

 of a rigid rod and sail — the rod representing the stiff anterior 

 margin of the wing ; the sail, which is made of paper bordered 

 with card-board, the flexible posterior portion. The other 

 wing consists of a rigid nervure in front and behind of thin 

 parchment which supports flne rods of steel. He states, that 

 if the wing only elevates and depresses itself, " the resistance 

 of the air is sufficient to produce all the other movements. 

 In eff*ect the wing of an insect has not the power of equal 

 resistance in every part. On the anterior margin the extended 

 nervures make it rigid^ while behind it is fine and flexible. 



