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there may be a deposition of dew upon the silk, to the extent, even,
of several hundred pounds; ballast has then to be thrown out, or the
machine may descend. This ballast being discarded, and a clear sunshine
evaporating the dew, and at the same time expanding the gas in the silk,
the whole will again rapidly ascend. To check this ascent, the only
recourse is, (or rather was, until Mr. Green's invention of the
guide-rope,) the permission of the escape of gas from the valve; but, in
the loss of gas, is a proportionate general loss of ascending power; so
that, in a comparatively brief period, the best-constructed balloon must
necessarily exhaust all its resources, and come to the earth. This was
the great obstacle to voyages of length.
"
The guide-rope remedies the difficulty in the simplest manner
conceivable. It is merely a very long rope which is suffered to trail
from the car, and the effect of which is to prevent the balloon from
changing its level in any material degree. If, for example, there should
be a deposition of moisture upon the silk, and the machine begins to
descend in consequence, there will be no necessity for discharging
ballast to remedy the increase of weight, for it is remedied, or
counteracted, in an exactly just proportion, by the deposit on the
ground of just so much of the end of the rope as is necessary. If,
on the other hand, any circumstances should cause undue levity, and
consequent ascent, this levity is immediately counteracted by the
additional weight of rope upraised from the earth. Thus, the balloon
can neither ascend or descend, except within very narrow limits, and its
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