Another ascent was arranged for the 14th of August, in which Robertson was to be accompanied by the professor, but the latter, yielding to the entreaties of his family, did not go. “I went up with my friend Lhoest,” says Robertson, “at forty-two minutes past twelve midday. 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.
“The wind continuing to carry me towards the sea, I resolved to bring my observations to an end. I effected my descent in a meadow, near the village of Rehorst, in Holstein, after having run sixteen leagues from France in sixty-five minutes.”
At the commencement of the year 1804, Laplace, at the Institute, proposed to take advantage of the means offered by aerostation to verify at great heights certain scientific points—as, for example, those which concern magnetism. This proposition was made at a favourable time, and was, so far, carried out in the best possible way. The aeronauts who were appointed to carry out the expedition were Biot and Gay-Lussac, the most enthusiastic aeronauts of the period.
The following is their report:—
“We observed the animals we had with us at all the different heights, and they did not appear to suffer in any manner. For ourselves, we perceived no effect any more then a quickening of the pulse. At 10,000 feet above the ground we set a little green-finch at liberty. He flew out at once, but immediately returning, settled upon our cordage; afterwards, setting out again, he flew to the earth, describing a very tortuous line in his passage. We followed him with our eyes till he was lost in the clouds. A pigeon, which we set free at the same elevation, presented a very curious spectacle. Placed at liberty on the edge of the car, he remained at rest for a number of instants, as if measuring the length of his flight; then he launched himself into space, flying about irregularly, as if to try his wings. Afterwards he began his descent regularly, sweeping round and round in great circles, ever reaching lower, until he also was lost in the clouds.”
As to the voyagers themselves, this is how they speak of their situation at the height of 3,000 yards:—
“About this elevation we observed our animals. They did not appear to suffer from the rarity of the air, yet the barometer was at twenty inches eight lines.. We were much surprised that we did not suffer from the cold; on the contrary, the sun warmed us much. We had thrown aside the gloves which had been put on board, and which were of no use to us. Our pulses were very quick; that of M. Gay-Lussac, which is 62 in the minute on ordinary occasions, now gave 80; and mine, which is ordinarily 89, gave 111. This acceleration was felt by both of us in nearly the same proportion. Nevertheless, our respiration was in no way interfered with, we experienced no illness, and our situation seemed to us extremely agreeable.”
The following is their report to the Galvanic Society—