BALLOON ASCENTS. 411 
obscured by cloudy a space of fully 1^000 feet bad to be passed 
for a decline of 1°. 
Up to 5^000 feet tbe results are based upon experiments 
varying from 13 to 22; at 6_,000 and 7,000 feet to 7 and 5 
respectively; from 7,000 to 16,000 to 4 only; these having 
been made on two days in 1863, June 26 and September 29^ 
on which days the balloon was frequently enveloped in fog 
and clouds to the height of three and four miles, and those 
above 16,000 feet on the former of these two days only, 
during the ascent and descent; the sky being still covered 
with cloud, when the balloon was between four and five miles 
high. 
I may here remark upon the fact of passing through 
clouds situated three and four miles high, and finding clouds 
higher still. Clouds of a dense character were previously 
supposed to be always located very much nearer the earth ; and 
to one class of clouds alone, viz. the cirrus, commonly called 
mares^ tails, was attributed elevations at such great heights. 
With clear skies the decline of temperature within the first 
1.000 feet was 6J° ; in the next, 4f° ; and decreasing con- 
tinually with elevation, till at 27,000 feet the decrease in 1,000 
feet was 1° only. Up to the height of 22,000 feet, the number 
of experiments had varied from 7 to 17 in each step of 1,000 
feet, and there can be but little doubt that the numbers result- 
ing from so many experiments are very nearly true. 
The space necessary to pass through for a dechne of 1° of tem- 
perature, is less than one hundred feet near the earth ; averag*- 
ing 162 feet for the first 1,000 feet, and at heights exceeding 
25.000 feet, it is necessary to pass through 1,000 feet of verti- 
cal height, for a decline of 1° of temperature. 
I have endeavoured, thus far, to give the results for tem- 
perature. They differ in both states of the sky from the results 
found from mountain observations, and, consequently, this 
value can no longer be used in any physical investigations 
where needed. Without exception, the fall of 1° has always 
taken place in the smallest space when near the earth, and the 
space continually increases the farther removed from the earth. 
These results were those based upon summer observations, 
made when the sun was well up, or during the hours of the 
day. A question then arose, Will the same laws hold good in 
all seasons of the year, and will the laws during the day be 
true at night in that season of the year ? To answer these 
questions, experiments have been made in different seasons, 
and at different hours of the day. It was found, even in 
summer, that the rapidity of the decrease was checked for 
some time before sunset, and that, on one occasion, in the 
month of June, there was found to be no difference of 
