FLIGHT AND FLYING MACHINES. 501 
power. I think you will see that in any case this renders it utterly im- 
possible for a man to navigate the air by his own exertions; but if 
there is anything more wanted to demonstrate the fact, we might 
deduce the same result from the experiments of Herr Lilienthal, which 
I hope to consider later, in which he starts from the top of a hill and 
goes sailing down through the air under gravity. If instead of sailing 
in a downward path a man wanted to fly horizontally, he would have to 
exert as much horse-power as would enable him to run wp the hill carry- 
ing the flying machine with him, in the time that the flying machine takes 
to descend to the bottom. As the apparatus descends fairly rapidly, you 
will realize that it would be impossible for a man to run up a hill 
carrying the weight of the flying machine while Herr Lilienthal was 
descending, and consequently it would be impossible for a man to drive 
himself through the air. 
But if itis impossible for man to fly by his own exertions we now know 
that he can construct machines which will produce a far greater horse- 
power in proportion to their weight than any bird can produce, and for 
this reason I consider that the problem of flight, at the present time, 
is entirely different from that which had ‘to be solved in the times of 
Bacqueville and Pétin and all those amusing old Frenchmen. Mr. 
Thorneycroft has built a large torpedo-boat destroyer, which exerts one 
horse-power for every 191 lbs. weight. That weight per horse-power 
is less than some birds have; but we are not justified in saying that 
the vessel could fly if it were furnished with wings, for horse-power 
per lb. or weight per horse-power is not the only factor on which the 
possibility of flight depends. It does not follow that when you increase 
the size of a bird or of a flying machine 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, a very simple piece of calculation 
by elementary mechanics will show that if all the dimensions of an 
animal be quadrupled it would have to exert double the horse-power 
per lb., (not double the actual horse-power, but to double the horse- 
power for every pound of its weight) to sustain itself in flight, so that 
large animals and large flying machines would require greater horse- 
power per lb. than small ones. 
We will now consider Mr. Maxim’s attempts to construct a light and, 
at the same time, powerful engine, which have led to such successful 
results from his experiments. Mr. Maxim used steam power and he 
generates it by a combustion of naphtha. His furnace is provided with 
a very large number of burners (700 or more) so as to give the largest 
possible area of flame. The boiler is a water-tube boiler, consisting of 
of an enormously large number of fine tubes for generating steam in 
order to get the largest production of steam in the smallest space, and 
as for the engines they are so light that Mr. Maxim can easily lift them 
in his hands. The total weight of his machine is about 8,000 lbs., and 
he reckons that it does not weigh more than 11 Ib. per horse-power. 
Now when you come to think of the birds weighing 150 to 200 lbs. per 
