V 



ON THE STEADY MOTIONS OR THE AVERAGE CONDI- 

 TION OF THE EARTH'S ATMOSPHERE 



BY PROF. DR. ADOLPH ERMAN 



In the third book of his Mecanique Celeste, Laplace has demon- 

 strated that the atmosphere of a rotating planet is at rest relative 

 to any point of the solid nucleus of this planet and that at the same 

 time any pressure and any density can occur within any level sur- 

 face of such an elastic fluid, i. e., within any surface that at any 

 point is normal to the resultant of gravity and centrifugal force. 

 In this he assumes that a uniform temperature prevails throughout 

 the elastic fluid. 



The surface of the sea is such a level surface and apparently on 

 the strength of the above demonstration by Laplace most physicists 

 assume that the product of gravity by the height of the barometric 

 column 2 which measures the pressure of the air must necessarily 

 be the same everywhere at sea level. They grant that temporary 

 disturbances of the atmospheric equilibrium are accompanied 

 by temporary interruptions of this uniformity of atmospheric 

 pressure, but imagine that these two exceptions are only periodical 

 (viz: variations about a mean condition) which mean must be 

 primarily a condition of rest relative to the earth, and secondarily 

 must be that uniform mean reduced barometric height that one 

 should find from measurements taken during one or many whole 

 years at different points on the earth's surface. 



The falsity of every portion of these assumptions was shown 

 many years ago and should have been evident a priori still earlier. 



I have found the mean reduced barometric readings for different 

 localities at sea level extremely different. Among others, for in- 

 stance, the pressure at the polar limits of the two trade wind belts 

 is from two to three Paris lines (0.18 to 0.27 English inches) greater 



1 Translated from the Astronomische Nachrichten, No. 1680, February, 

 1868, Vol. LXX, cols. 369-378. 



2 For brevity I will call this product the reduced barometric height or 

 the pressure of the air. 



3 1 



