542 



SCIENTIFIC RECORD FOR 1883. 



height at which pressures are the same over both localities will be given 

 approximately by . 



h=(\ogB— logB,) 



72 T T, 



T, — T 



where T = 250 + t + S2 (60-5 — <p) and similarly for T^ ; or if we neg- 

 lect the effect of difference of latitude we get approximately 

 , /jo k B — Bi T Ti 



* = w - 5 tt=t • B+1T, 



or assuming the lower pressure to be not far from 750 mm. we have 



where C varies from 2,000 at — G°C. to 3,000 at + 12QC. 



For convenience iu acquiring a permanent remembrance of the dis- 

 tribution of the atmosphere and the relative importance of the masses 

 of successive strata, Koppen gives the following table showing the air 

 temperature, vapor tension, and barometric pressure at successive alti- 

 tudes, so chosen that between each there is contained one-sixth of the 

 weight of the atmosphere. 



The temperatures are determined by the admirable formula of Men- 

 delieff, which applies especially to the free air and great altitudes, aud 

 in whicli, however, Koppen adopts the constant 40° from Hann, instead 

 of the 30° given by Mendel ieff, whence it becomes 



t b + 40° __ bh 

 U + 40o - B 



The vapor tension is given on the assumption that the air is satu- 

 rated at the temperature given for each altitude. 



Koppen enforces careful attention to the fact that sensible horizontal 

 and vertical gradients of pressure have each their respective import- 

 ance iu the atmospheric motions, lie attributes both to differences of 

 density, due mostly to temperature; differences in a horizontal direc- 

 tion give rise to the general atmospheric circulation and the extensive 

 storms; differences in a vertical direction (i. c, departures from a 

 condition of stable equilibrium) give rise to local motions, such as form 



