FLIGHT AND FLYING MACHINES. 493 
Let us consider, in the first place, how animals learnt to fly. It may 
be stated, as a fundamental fact, that small animals found it much 
easier to learn to fly than large ones. M. de Lucy prepared a table 
giving the area of wing surface of large and small animals for every 
kilogramme of weight supported, that is, he divided the area of wing 
surface (in square yards or square feet) by the weight of the animal 
in kilogrammes. His table shows that large animals have a much 
smaller amount of wing surface in proportion to their weight than 
small ones. ‘The crane of Australia has only 130 square inches per 
kilogramme, whereas a bat has 11 square inches. 
The general law connecting the area of the wing surface with the 
weight may be very simply expressed. Suppose that we double the size 
of an animal and make it exactly of the same shape as before, so that its 
various parts have the same proportions, then the superficial area of the 
wings will be increased fourfold, but the weight will be eight times as 
great, so that the area of wing surface per kilogramme will be half as 
great as before. This law of relation, M. de Lucy found, was approxi- 
mately verified by actual observation, and hence it follows that large 
flying animals are (roughly) similarly proportioned to small ones. As- 
suming this to be the case, we may prove that small animals (such as 
insects) must have found it much easier to learn to fly than large ones, 
the reason being that they were not exposed to the same risks and 
dangers. In the first place it is popularly supposed that a flea, if mag- 
nified to the size of a man, would be able to jump over the top of St. 
Paul’s; asa matter of fact that is not the case; it would jump to precisely 
the same height as it does now. Of course, it would be capable of ex- 
erting much greater energy in jumping, but then it would have to lift 
a proportionately greater weight, and so it would lift itself to just the 
same height by exerting the same amount of energy in proportion to its 
weight. Similarly, a small animal, if it were to fall to the ground from 
the height of say a yard, would sustain about the same proportionate 
amount of injury from the effects of the fall as a large one, supposing 
both to strike the ground with the same velocity. Nowa small insect 
would have room to fly in a height of a few inches, to a foot or so above 
the ground ; but a large animal would require a considerably greater 
height to fly in; so that the injury from an accident would be much 
less for a small than a large animal. Ifa small insect falls through a 
few inches, it will not hurt itself much, but if we were to construct an 
artificial flying machine, this machine would have to be made so large 
that we should have to rise to a height of at least 20 feet from the 
ground before we could expect to attain any useful results,and a fall from 
a height of even 20 feet would be, to say the least, highly dangerous. 
We may, however, even go further and state that a fall from a height 
of 20 feet would not do the same harm to a beetle or a small insect that 
it would do to a larger body, because of the effects of the resistance of 
the air in checking the fall. In illustration of that, I have arranged 
an experiment to show you that small bodies, allowed to drop from a 
height, are more retarded by the resistance of the air, and therefore 
descend more slowly than large ones. I have fixed to the ceiling three 
pieces of paper, one of them is a small square, another one cut out from 
