378 



SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 



atmospheric stratum, and from the deduction of a similar law for the 

 temperature. 



But if we examine the vapor-tensions for different altitudes as given 

 by Strachey, we are surprised at the agreement on the one hand be- 

 tween the results of the observations that Welsh made during his bal- 

 loon voyages and those that Hooker and Strachey made in the Hima- 

 layas, and on the other hand at the agreement of the latter among them- 

 selves, especially at the greater altitudes. This unexpected fact induced 

 me, following Strachey's steps, to compute the observations of Glaish- 

 er's balloon voyages; and since the figures thus obtaiued agreed very 

 satisfactorily with those of Strachey, I collected also the material known 

 to me relative to observations of humidity at fixed stations at greater 

 mountain altitudes. Thus the following table has resulted. Like 

 Strachey, I have expressed the vapor-tension at a given altitude in a 

 fraction of that simultaneously observed at or near the earth's surface. 



Since the altitudes for which observations are at hand seldom agree 

 with the intervals of the table, therefore the required quantities for the 

 nearest tabular interval were computed, by a formula, hereafter given, 

 from the observed values. 



Diminution of Vajior-tension with Altitude. 



(The bracketed numbers have only one-half weight.) 



The following are the observations on which are based each individual 

 series of the above table. 



Himalaya. — {a) Observations by Hooker : (&) by Strachey, extracted 

 irom the above-cited memoir ; (c) annual means of observation at Maha- 

 baleshwar and Bombay ; at Darjeeling and Goalpara ; at Dodabetta and 

 Madras. 



Armenia. — Observations by Moritz during his ascent of the Greater 

 ^^rarat in August, 1850, published in Kupffer's Correspondance Miteoro- 

 logique, annee 1858. Moritz took hourly observations of nearly all the 



