48 



ON MAGNITUDE 



[CH. 



the normal anatomy of a bird, becomes physiologically impossible. 

 The same reasoning applies to the case of man. It would be very 

 difficult, and probably absolutely impossible, for a bird to flap its 

 way through the air were it of the bigness of a man; but Borelli, 

 in discussing the matter, laid even greater stress on the fact that 

 a man's pectoral muscles are so much less in proportion than those 

 of a bird, that however we might fit ourselves out with wings, we 

 could never expect to flap them by any power of our own weak 

 muscles. Borelli had learned this lesson thoroughly, and in one of 

 his chapters he deals with the proposition : Est impossibile ut homines 

 jyropriis viribus artificiose volare possinV^, But gliding flight, where 



a ' b 



2. Fairy-flies (Mymaridae) : after F. Enock. x 20. 



wind-force and gravitational energy take the place of muscular 

 power, is another story, and its limitations are of another kind. 

 Nature has many modes and mechanisms of flight, in birds of one 

 kind and another, in bats and beetles, butterflies, dragonflies and 

 what not ; and gliding seems to be the common way of birds, and 

 the flapping flight {remigio alarum) of sparrow and of crow to be 

 the exception rather than the rule. But it were truer to say that 

 gliding and soaring, by which energy is captured from the wind, are 

 modes of flight little needed by the small birds, but more and more 

 essential to the large. BorelH had proved so convincingly that 

 we could never hope to fly propriis viribus, that all through the 

 eighteenth century men tried no more to fly at all. It was in trying 

 to glide that the pioneers of aviation, Cayley, Wenham and Mouillard, 



* Giovanni Alfonso Borelli, De Motu Animalium, i, Prop, cciv, p. 243, edit. 

 1685. The part on The Flight of Birds is issued by the Royal Aeronautical Society 

 as No. 6 of its Aeronautical Classics. 



