SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 6 i i 



shows, from the observations of Hooker aud his own iu the Himahiyas, 

 as well as from those that Welsh made iu four balloon voyages, that the 

 absolute humidity (or the vapor- tension) diminishes in a much more 

 rapid ratio with the altitude thau would be the case iu an independent 

 atmosphere of vapor subject to its owu pressure only. He then further 

 shows that the existence of an independent vapor atmosphere is excluded 

 by the rate of diminution of temperature with altitude as deduced from 

 all known observations considered together with the vapor-tension 

 observed at the surface of the earth. This latter proposition had already 

 been mathematically demonstrated by Bessel iu 1838.* Of course 

 Strachey concludes further that it is not admissible to subtract the 

 vapor-tension from the barometric pressure in order to obtain the i)ressure 

 of the dry atmosphere.t By means of an estimate based upon Hook- 

 er's and Welsh's observations, Strachey finds that the actual pressure 

 of the vapor iu the atmosphere is to the tension observed at the earth's 

 surface as 1 to 4. Lamont arrived at the result 1 to o, nearly agreeing 

 therewith, by making Glaisher's observations the base of his computa- 

 tion.! 



Strachey does not attempt to deduce a formula for the diminution of 

 vapor-pressure with altitude from the vapor-tensions at different alti- 

 tudes in the atmosphere, as communicated by him; and Lamont has, iu 

 the above-cited memoir, expressed his conviction of the non-existence of 

 any regular change of vapor-pressure with altitude. This is, indeed, a 

 necessary consequence of the denial of Daltou's vapor atmosphere; 

 according to this view, the atmosphere of vapor never arrives at that 

 condition of equilibrium which is assumed for it by Dalton's proposition 

 of an independent gaseous atmosphere. At the earth's surface, at higher 

 temperatures, aqueous vapors are developed of greater tensions than 

 would correspond to the possible vapor- tensions that obtain at the lower 

 temperatures iu the higher strata of the air. The slow diffusion of 

 aqueous vapor in the air alone prevents its rapid continued condensa- 

 tion in the upper strata. By reason of ascending currents of air, as well 

 as any other cooling of masses of moist air, there occur, now here and 

 now there, condensations of vapor ; and under such conditions the 

 existence of a state of equilibrium in the vapor atmosphere cannot 

 be assumed. Were oxygen and nitrogen continually produced, and at 

 lower temperatures again locally condensed in the same proportions as 

 is the aqueous vapor, then a barometric measurement of altitude would 

 be out of the question. AVe must then a priori refrain equally from the 

 deduction of any law permitting one to determine the vapor-pressure at 

 any higher or lower altitude from the vapor-tension observed iu any 



* Remarks on Barometric Hypsometry, Astron. Nach., Band 16, No. 356. 



tAYe expressly say "atmosphere," since it is of course permissible for physical pur- 

 poses to subtract the vapor-teusion from the barometric pressure in order to obtain the 

 ■weight or the pressure of the dry air within a definite space. 



\ See this Journal, iii, 291. 



