180 



SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 



altitude, the above altitude must be different ; <f{t) and <f{g) indicate the 

 correctional factors. For dry air, free from carbonic acid gas, C is 7,992 

 meters, and since the density of aqueous vapor may be assumed con- 

 stant at 0.623 for ordinary atmospheric temperatures, therefore for an 

 atmosphere of aqueous vapor G = 12,829 meters. We therefore have 

 the following- formula for the computation of the pressure at any alti- 

 tude within an atmosphere of aqueous vapor, and omitting the small 

 corrections, 



nat \osi) = nat logj^o - -j^^^ 5 

 or, multiplying by the modulus of the Briggs logarithms, 



log p = log po 



1^9539 ' 



This formula can be used at once to compare the observed diminution 

 of vapor-tension with that which must obtain in an independent atmos- 

 phere of aqueous vapor. Up to an altitude of 20,000 English feet, or 

 0,096 meters, the correction <f{g) can be neglected, and the introduction 

 of <f(t) = l-[-at would have the eiiect of still further delaying the dimi- 

 nution of tension up to about 12,0C0 feet. 



Thioreilcal and Observed Diminutions of Vapor-tension. 



Altitudes in thousands of Englisli feet. 



16 20 



p compiited. 

 p observed.. 



1.00 

 1.00 



0.91 

 0.64 



0.83 

 0.42 



0.75 

 0.27 



0.68 

 O.lrf 



0.G2 

 0.13 



Whence the vapor-tension actually does diminish with the altitude 

 much more rapidly than would be the case if an independent gaseous 

 atmosphere existed. 



As before remarked, Bessel had ah^eady, through a roundabout and 

 involved computation, proven that the slow diminution of vapor-tension 

 with the altitude, as is required in Dalton's vapor atmosphere, can- 

 not possibly be reconciled with the known diminution of temperature, 

 for aqueous vapor has a definite maximum of elastic force for each tem- 

 perature. Our above-written formula must therefore also satisfy the 

 conditions 



- h 7.447.') t 



p=:po 10''iy5;i9 and jf equal or less than 4.525 x lO-^^'^s'-ff. 



The last member on the right is the formula given by Magnus for the 

 maximum tension of aqueous vapor for a given temperature t. Hence 

 follows 



, ^ r. ^--^r^ 7.4475^0 I ^1' 



log Po == or < 0.GOOG2 + ,;,,.,, _^,„ + ^nj^j 



