DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 



409 



is scarcely necessary to add, that in the aero-planes and aerial screws, as at 

 present constructed, no provision whatever is made for suddenly increasing or 

 diminishing the sustaining area, of conferring elasticity upon it, or of giving to the 

 supporting surfaces that infinite variety of angles which would -enable them to seize 

 and disentangle themselves from the air with rapidity. Many investigators are 

 of opinion that flight is a question of mere levity and power, and that if a 

 machine could only be made light enough and powerful enough, it must of 

 necessity fly, whatever the nature of its flying surfaces. A grave fallacy lurks 

 here. Birds are not more powerful than quadrupeds of equal size, and String- 

 fellow's machine, which, as we have seen, only weighed 12 lbs., exerted one-third 

 of a horse power. The probabilities therefore, are, that flight is dependent to a 

 great extent on the nature of the flying surfaces, and the mode of applying those 

 surfaces to the air. 



Artificial Wings (Borelli's Vieivs). — With regard to the production of flight 

 by the flapping of wings, much may and has been said. Of all the methods yet 

 proposed, it is unquestionably by far the most ancient. Discrediting as apocry- 

 phal the famous story of Daedalus and his waxen wings, we certainly have a 

 very graphic account of artificial wings in the " De Motu Animalium " of 

 Borelli, published as far back as 1680, i.e., nearly two centuries ago.* 



Indeed it will not be too much to affirm, that to this distinguished physiologist 

 and mathematician belongs almost all the knowledge we at present possess of 

 artificial wings and their actions. He was well acquainted with the properties 

 of the wedge, as applied to flight, and he was likewise cognisant of the flexible 

 and elastic properties of the wing. To him is to be traced the purely mechanical 

 theory of the wing's action. He figured a bird 

 with artificial wings, each wing consisting of a rigid 

 rod in front and flexible feathers behind. I have 

 thought fit to reproduce Borelli's figure, both be- 

 cause of its great antiquity, and because it is emi- 

 nently illustrative of his text.t 



The wings, as a reference to fig. 54 will show, 

 are represented as striking vertically downwards 

 (g h). They remarkably accord with those describ- 

 ed by Straus-Durckheim, Girard, and quite recently by Professor Marey.J 



Borelli was of opinion that flight resulted from the application of an inclined 

 plane, which beats the air, and which has a wedge action. He, in fact, endeavours 

 to prove that a bird wedges itself forward upon the air by the perpendicular 



Fie. 54. 



Borelli. De Motu Animalium. Sm. 4to. 2 vols. Ronue 1680. 

 T " De Motu Animalium," Lugduni Batavorum apud Petram Vander. Anno mdclxxxv. Tab. 

 XIII. figure 2. (New edition.) 



% Revue des Cours Scientifiques de la France et de l'Etranger. Mars 1869. 



