It is of interest to notice that the law is reversed in
the case of a body which is not supported by the resistance of a
fluid in which it is immersed, but floats in it, the ship or
balloon, for example. When we double the linear dimensions of a
steamship in all its parts, we increase not only her weight but
her floating power, her carrying capacity, and her engine capacity
eightfold. But the resistance which she meets with when passing
through the water at a given speed is only multiplied four times.
Hence, the larger we build the steamship the more economical the
application of the power necessary to drive it at a given speed.
It is this law which has brought the great increase in the size of
ocean steamers in recent times. The proportionately diminishing
resistance which, in the flying-machine, represents the floating
power is, in the ship, something to be overcome. Thus there is a
complete reversal of the law in its practical application to the
two cases.
The balloon is in the same class with the ship. Practical
difficulties aside, the larger it is built the more effective it
will be, and the more advantageous will be the ratio of the power
which is necessary to drive it to the resistance to be overcome.
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