In a minute or two we rose up between two
masses of cloud, which seemed to open up and offer us a passage.
The upper surfaces of these clouds are not uniformly level, like
the under sides seen from the earth, but they are of a conical or
pyramidal shape. These imposing masses seem to precipitate
themselves upon the earth, as if to engulf it, but this optical
illusion was due to the apparent immobility of the balloon, which
at the moment was rising at the rate of about twenty feet per
second.
"The fear of losing the view of the Baltic, which we perceived
between the clouds at intervals, obliged us to renounce the
project of rising as high as on the last occasion. The barometer
was at fifteen inches, and the thermometer one degree below zero,
when I let off two pigeons.
"One descended in a diagonal direction, its wings half open but
not moving, with a swiftness which seemed that of a fall. The
other flew for an instant, and then placed itself upon the car,
and did not wish to quit us. Acting on the hint of Dr. Reimarus,
I tried the same experiment with butterflies, but the air was too
much rarefied for them; they attempted in vain to raise
themselves by their wings, but they did not forsake the car.
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