4.92, FLIGHT AND FLYING MACHINES. 
designing their machine, taking it for granted that it would fly when 
constructed, in other words they thought they would be able to fly 
without learning ; and it is only quite lately that people have realised 
the necessity of learning to fly first, 7.e., learning the laws of flight 
before building a flying machine, which of course is the natural order 
to follow. 
As flying is a form of locomotion, let us first consider the problem of 
locomotion generally. The fundamental principle underlying every 
form of locomotion is involved in Newton’s “‘ Third Law of Motion,” 
which states that action and reaction are equal and opposite. One of 
the simplest illustrations of this law, and one with which every artillery 
officer is familiar, is that afforded by the recoil of a gun. A bullet 
cannot be fired without making the gun recoil, and the problem to be 
solved in the construction of guns is, to get as much as possible of the 
energy produced by the combustion of the gunpowder usefully em- 
ployed in driving the bullet forwards, and as little of it as possible 
wasted in driving the gun backwards. In order to accomplish this, we 
must make the gun as heavy as possible and the bullet very light, for 
the heavier the gun and the lighter the bullet, the greater will be the 
proportion of the energy imparted to the bullet; in fact, the energies of 
the gun and bullet are inversely proportional to their masses. Sup- 
posing, therefore, that the gun is one hundred times the mass, 2.e., one 
times the weight of the bullet, then the bullet will have one hundred 
times the energy of the gun, that is, one hundred times the power of 
doing damage. ‘Thus, that if we put one hundred and one ounces of 
gunpowder into the gun, only one ounce will be wasted in producing 
recoil, and one hundred ounces will be used in propelling the bullet. 
In the case of locomotion we and our vehicle take the place of the 
bullet, and the earth, the water, or the air takes the place of the gun, 
according as we are travelling by land, water, or flying. The inference 
is that the mass that we act on must be made as great as possible so as 
to utilize as much energy as possible in moving ourselves forward. In 
walking, the action of our feet tends to drive the earth back, and the 
reaction of the earth, which is equal and opposite to this action, tends 
to move us forwards. Here, practically, the whole of the energy we 
exert is usefully employed in producing locomotion, for the mass of the 
earth is so enormously large that we do not communicate any ap- 
preciable energy toit. In swimming, we drive the water backwards 
and its reaction impels us forwards ; similarly in flying, we should have 
to drive the air backwards and downwards; in order that its reaction 
may impel us forwards and upwards, we must act on as large a mass of 
earth, or of water, or of air as we can. To illustrate the difference 
between locomotion on land, locomotion in water and locomotion in air, 
we may compare such animals as the ox, the porpoise and the bat, 
which have been chosen by Pettigren in illustration of the subject. 
For swimming, fairly large appendages are required by the porpoise in 
order to act on a considerable mass of water; but air is so much 
lighter than water, that in order to fly a bat has to have far larger 
wings in proportion to its size; and a similar difference would have to 
exist between the construction of flying machines and of steamships. 
