SHOET MEMOIRS ON METEOEOLOGICAL SUBJECTS. 385 



the air remains quite uuiform iu dififerent altitudes. Therefore, the 

 vapor-tension depends only on the diminution of temperature. If this 

 latter proceeds in an arithmetical progression, there follows, of course, 

 for the diminution of vapor-tension a geometric progression. Only the 

 demonstration may be new, that we can also, with so great accuracy, 

 from observations at one altitude, compute also the mean vaiiortension 

 at another altitude. 



B. 



ON THE INFLUENCE OB^ RAIN UPON THE BAROMETER, 

 AND UPON THE FORMATION OF PRECIPITATION IN 

 GENERAL. 



By Dr. J. Hanx. 



[Trauslated by Clevelaud Abbe from the Journal of the Austrian Meteorological Association, 1874, pp. 



289 et seq.] 



A more accurate knowledge of the influence which the condensation 

 of the aqueous vapor in the atmosphere exerts npon the disturbances 

 of its equilibrium and upon the changes of atmospheric pressure is at 

 present of special importance, since, in the theory of storms, we have 

 to a certain degree returned to the views of Espy.^ This may be our 

 excuse that we once more return to this subject after having, in a i^re- 

 vious volume of our periodical,^ given place to a discussion upon this 

 subject. At that time I had to refer to the contradiction that appeared 

 to exist between the theory and the computations of Espy, Kronig, and 

 Reye and the observed facts. According" to Espy and Reye, the con- 

 densation of vapor into cloud and rain produces a considerable fall in 

 pressure under the place where the rain falls. But every careful ob- 

 server knows, on the other hand, that the tendency of rainfall appears to 

 be rather to increase the pressure. The barometer rises during the rain, 

 and after the rain stands higher than before. If the rain had the effect 

 computed by Reye, to diminish the iiressure, or even a much less effect, 

 then would the reverse take place. It, indeed, rains generally during 

 low pressures J but the lowest barometer precedes the rainj — if it were 

 a consequence of the rain, it would occur during or after the rainfall. 

 Reye has had the kindness to go into the discussion of this point, and 

 thereby has in great part removed the apparent contradiction between 

 computation and observation.^ He allows that, in the case where the 

 precipitation is produced by the inflow of colder air or by radiation or 

 conduction of heat, and where the latent heat of condensation is thus 

 neutralized, the pressure can rise during the rain ; that equally, in the 

 case where new masses of air steadily flow toward the place of precipi- 

 tation (the rainfalls of a moist current of air blowing over a mountain), 

 the formation of a barometric minimum will be hindered. But if we 

 now consider the remaining causes of the formation of precipitation, we 

 25 S 



