458 
AEROSTATION. 
which they were then floating-, and the almost total consumption of 
their ballast, and the continual though gradual and slow sinking of the 
balloon, induced Mr. Robertson to reject this proposal. — As the aero- 
nauts were now floating over some towns or villages, Mr. Sacharof 
took his speaking trumpet, and directing it towards the earth, called, 
as loud as he was able, when, contrary to his expectations, he heard 
his own words after a considerable interval, clearly and distinctly 
repeated by an echo ; he called out again several times, and each 
time the echo repeated his words in about ten seconds : at this time 
the barometer was removed, for the purpose of descending, so that he 
could make no observation upon it ; but computing by the sup^ 
posed velocity of sound, he must then have been about five thousand 
seven hundred feet from the earth. 
In order that the descent might be made as safely as possible, and 
for the sake of security, all the instruments and warm clothing were 
tied up in a bundle, and let down, together with an anchor, bv a rope. 
The balloon, which w'as driven by the wind with considerable force, 
and fell with great rapidity, was, notwithstanding, so light, that when 
the bundle reached the earth, and the machine was in part divested 
of this load, it had a tendency to rise ; in the mean time, how ever, 
Mr. Robertson suffering the gas to escape, the descent was ultimately 
effected in the gentlest and pleasantest manner possible, at about 
forty-five minutes past ten, on the estate of Counsellor Demidof; but 
it unfortunately happened, by the bundle being drawn for a consider- 
able distance along the ground, that most of the instruments were 
destroyed, and only four of the eight casks that had been charged, 
were in a state proper for experiment. 
We have given the detail of the two preceding ascents, not in conse- 
quence of the importance of the observations or experiments that 
were performed in them, but because they seem to have been the 
first aerial excursions made purely with a view to philosophical re- 
search, and, moreover, because in some respects the inferences to be 
drawn from them are at variance with the deductions formed from the 
experiments performed in the two following ascents ; the first by 
Biot and Gay Lussac, and the second by the latter philosopher alone. 
M. Biot and Gay Lussac ascended from the Conservatoire des Arts, 
on the 24th of August, 1804, their principal object being to examine 
whether the magnetic power experienced any appreciate diminution 
as we ascend from the terrestrial surface. It seems from the account 
given by Messrs. Sacharof and Robertson, that there was at least a 
change in the dipping power ; and Saussure, from experiments made 
on the Col du Geant, at the height of three thousand four hundred 
and thirty-five metres above the level of the sea, thought he could per- 
ceive a very sensible decrease of magnetic virtue, which he estimated 
at one-fifth. It had even been asserted by some aeronants, that the 
magnetic energy vanishes entirely at a certain height ; and it appear- 
ed important to many members of the institute to ascertain the truth 
or fallacy of these assertions ; and Saussure, in particular, was anxious 
that his observations might be repeated in isolated situations, remote 
from any effect of local attractions. 
Besides the usual provisions of barometers, thermometers, hygro- 
