90

Classification of the Sci
90

force is diminished in the same proportion and the rate of increase of the upward velocity becomes less and less. Neglecting the resistance of the air, which is not great, especially with the new plan of making the top part of the balloon conical, the maximum upward velocity is attained when the ascensional power is precisely equal to the weight carried. But nothing can prevent the balloon from rising far higher, losing gas all the time, until when the upward velocity ceases, it is far heavier than the air and if allowed to descend would do so with velocity constantly accelerated (neglecting the resistance of the air) until it struck the ground. To prevent this, ballast is discharged; but the balloonist does not discover that the balloon is descending until its downward velocity is considerable. He does not want to throw out too much ballast, for he is high enough already. He does not know how much he ought to throw out, usually; although this ought to be prepared beforehand. He therefore lets it run out slowly and the consequence