150 ANNUAL OF SCIENTIFIC DISCOVERT. 



least 1,000 feet. If we now take the whole decrease of temperature 

 with elevation, we shall have the following results: From the ground 

 to 1,000 feet 7.2, or 1 in 139 feet. About 14,000, the average is the 

 same as would be given by using the mean as found from observations 

 on mountain-sides, namely 1 in 300 feet ; but at heights less and greater 

 than 14, 000' feet the space is less or greater than 300 feet. It is cer- 

 tain, then, in any balloon ascent, between 8,000 and 20,000 feet, if 

 the temperature on leaving the earth, and at the highest elevation, 

 were only used, that the results, 1 in 254 feet in the former, and 1 

 in 355 in the latter, would have been looked upon as generally con- 

 firming the theory of a decline of 1 in 300 feet, and hence the ne- 

 cessity of noting the temperature on leaving the earth, as frequent- 

 ly as possible afterwards, and extending the observations to the 

 highest point possible. It would appear from the results obtained 

 that the decline of temperature is largest near the earth, smallest at 

 the highest elevations, and intermediate with increasing spaces for the 

 same decrease of temperature, in these respects agreeing, therefore, 

 with the general law, as formed from the extreme high ascents. This 

 law seems to me more natural and consistent than a uniform rate of 

 decrease could be, received as a physical law, up even to moderate 

 elevations. But I have reasons to believe that the amount of change 

 is different at different seasons of the year, and I think it is different 

 during the night from that during the day. And it seems certain that 

 these Jaws will not hold good for all countries, although they probably 

 will for very large tracts of country. I have reason to believe they 

 will not hold good in India. 



From all the experiments made in the year 1862, it was found that 

 at the earth's surface there were upon the average very nearly five 

 grains of water in a cubic foot of air, in the invisible shape of vapor, 

 or l-50th part of a cubic inch of water ; or a cube of water whose 

 sides were a quarter of an inch nearly. This value decreased grad- 

 ually to one-half at the height of 5,000 feet, where there was only 

 l-100th of an inch of water in a cubic foot of air. At the height of 

 10,000 feet this amount was reduced to less than 1^ grain ; at 15,000 

 feet high there was only 9-10ths of a grain, or l-2SOth part of a cubic 

 inch; at 20.000 feet, this was reduced to half a grain; and at 25,000 

 feet to 1-1 Oth only of a grain or to a drop of water, = l-2530th part of a 

 cubic inch, being l-50th part only of the water at the surface of the 

 earth ; in other words, about a drop of water but little more than 1- 

 100th of an inch in diameter. But the actual amount met with on any 

 ascent will most probably differ from these results, as, like the temper- 

 ature of the air, the diffusion of water seems to be very rarely in a 

 normal state. The amount of water in the air at the same height 

 seems to be constantly varying, and to be affected with diurnal 

 changes, so that on comparing the moisture shown at one ascent with 

 that experienced in another, the time of day at which the experiments 

 were made will have to be considered. I have been speaking of the 

 amount of water actually present in the air. This information, with- 

 out reference to temperature, gives no'idea of the moisture of the at- 

 mosphere, since a capacity of air for moisture doubles itself for an in- 

 crease of about 20 of temperature ; a clearer idea of the relative 

 moisture at different heights will be given, by considering that amount 



