384 RECORD OF SCIENCE FOR 1887 AND 1888. 



" The systematic aud successful labors of meteorological observers iu 

 the last decade has given a series of empirical laws for the motion of 

 the air that have already become of great importance for meteorology 

 aud for weather predictions, and promise to become still more so in the 

 future. 



" In general the active forces that constitute the principal causes of 

 these phenomeua of motion have been correctly appreciated, but so far 

 as I know we have not yet been successful in bringing them into such 

 a systematic connection that we have been able to deduce therefrom a 

 mechanics of the atmosphere or a theory that reproduces the most im- 

 portant points iu the phenomena of motion. However, very noteworthy 

 attempts in this direction have already been made by dift'ereut parties. 



"The oldest investigations upon this point are due to the American 

 meteorologist, William Ferrel. They are contained in a large number 

 of memoirs, only a part of which is accessible to me ; but from the 

 memoirs that are known to me I think I may conclude that the most 

 important results to which Ferrel has attained are collected together 

 by himself in a work recently published (Recent Advances in Mete- 

 orology, Washington, or Ai^pendix 71 to the Annual Report for 1885 

 of the Chief Signal Officer), so that the following remarks relate to this 

 work: 



" Ferrel starts, in reality, with the equations of motion of a free heavy 

 point or a small free mass, and endeavors, by the addition of further 

 terms, to accommodate these equations to the motion of a fluid, but 

 without finally attaining the correct forui of the hydrodynamic equa- 

 tions. As effective forces he introduces the attraction of the earth, the 

 consideration of the differences of density of the air (iu consequence of 

 differences of temperature), the effects resulting from the rotation of 

 the earth, and, finally, the resistances of friction. 



" From the general equations he derives special solutions, in which, 

 first, the friction is neglected, and the additional assumption is made 

 that the currents in the directions of the small circles (parallels of lati- 

 tude) materially exceed in strength or velocity the movements in the 

 meridian that would take place on a motionless earth, iu consequence of 

 the differences in temperature between the tropics and the polar zones. 



" But such an assumption, in my opinion, ought not to be made with- 

 out further considerations. Rather is it the province of theory to dem- 

 onstrate its correctness, and to show for what reasons east and west 

 currents are stronger than the north and south currents. The com- 

 I)lete neglect of friction leads, as not otherwise to be expected, to for- 

 muhe that make the velocity at the poles become infinitely great, whence 

 follows that the atmospheric pressure will there be zero. The consider- 

 ation of friction, as to the method of whose action no special assumption 

 is made, has the result of mollifying these incorrect results and accom- 

 modating the phenomena of motion to the recogni/,ed sjiecia] «listril>n- 

 tioii of ])ressnre on the eartli surfac^e, 



