Count Zeppelin
After this four hours of flight, the wind suddenly changes to south-southwest. It now tends to carry the balloon to g in the next four hours. Meanwhile the balloon, heading west, overcomes the easterly drift, and the balloon actually lands at c. Unless there is some further favorable shift of the wind it cannot reach Albany. If, during the second four hours, its independent speed could have been increased to about fifteen and a half miles it would have just made it. The actual course has been fbc: a drifting balloon would have followed the course fdh, dh being a course parallel to bg.
GAS AND BALLAST
A cubical block of wood measuring twelve inches on a side floats on water because it is lighter than water; it weighs, if yellow pine, thirty-eight pounds, whereas the same volume of water weighs about sixty-two pounds. Any substance weighing more than sixty-two pounds to the cubic foot would sink in water.
Buoyant Power of Wood
If our block of wood be drilled, and lead poured in the hole, the total size of wood-and-lead block being kept constantly at one cubic foot, the block will sink as soon as its whole weight exceeds sixty-two pounds. Ignoring the wood removed by boring (as, compared with the lead which replaces it, an insignificant amount), the weight of lead plugged in may reach twenty-four pounds before the block will sink.