ARTIFICIAL FLIGHT. 539 



able address to the British Association at Nottingham. 

 Dr. Hauorhton reckons that men rowing- in a boat race 

 exert about one quarter of a horse-power, and if we take a 

 man weighing about twelve stone or 168 pounds, it follows 

 that he weighs 672 pounds per horse-power that he is able 

 to exert. Mr. Maxim, on the other hand, has proved that 

 heavy birds only weigh 1 50 pounds per horse-power that 

 they are capable of exerting ; so that they possess about 

 four times the horse-power per pound that we have. The 

 albatross and the vulture probably go up to 250 pounds 

 per horse-power. It thus appears impossible for man to 

 fly by his own exertions. 



But we are now able to construct machines which will 

 develop a far greater horse-power in proportion to their 

 weight than any bird. Ten years ago Mr. Thornycroft 

 built a large torpedo-boat (the Ariete) which exerted one 

 horse-power for every 191 pounds dead weight. This is less 

 weight per horse-power than some birds possess ; but we 

 are not justified in concluding that the vessel could fly if it 

 were furnished with wings, for horse-power per pound or 

 weight per horse-power is not the only factor on which the 

 possibility of flight depends. It does not follow that when 

 the size of a bird or of a flying machine is increased the 

 horse-power is directly proportional to the weight. That 

 law of proportionality in fact we know fairly well does not 

 hold. The horse-power must in fact increase more rapidly 

 than it would do if merely proportional to the weight. 

 Assuming that the resistance of the air is proportional to 

 the superficial area and to the square of the velocity, and 

 that flying animals of different sizes are similarly propor- 

 tioned, according to M. de Lucy's law (which is roughly 

 verified for birds and insects), a very simple piece of cal- 

 culation by elementary mechanics will show that if all the 

 dimensions of such an animal were quadrupled it would have 

 to exert double the horse-power per pound, or 128 times 

 the actual total horse-power, to sustain itself in flight. 

 Under similar assumptions large flying machines would 

 require greater horse-power per pound than small ones, the 

 general law being that the horse-power per pound is propor- 



