SKETCH OF WILLIAM FERREL. 693 



ies that Ferrel undertook, to be stopped only "by the illness tliat 

 caused his death. 



In 1882 Ferrel accepted a professorship in the Signal Service, 

 producing while there several special reports of high value, among 

 which his Recent Advances in Meteorology should have first men- 

 tion. He also lectured to the officers of the Signal Corps at Wash- 

 ington, and it is from these lectures that he subsequently prepared 

 his Popular Treatise on the Winds, the most comprehensive state- 

 ment of theoretical meteorology in the English language. He re- 

 signed this professorship in 188G, in his seventieth year. He had 

 before this accumulated a competence from judicious investments 

 of the small earnings of earlier years. 



Ferrel's name is chiefly connected with his original investiga- 

 tions in meteorology. The first of these was made at Nashville, 

 as stated above, but a more serious study was made in his Mo- 

 tions of Fluids and Solids relative to the Earth's Surface, pre- 

 pared shortly after going to Cambridge, and published in Runkle's 

 Mathematical Monthly. This is regarded by a most competent 

 critic as " the starting-point of our knowledge of the mechanics of 

 the atmosphere." It is here that he first clearly states the impor- 

 tant law that " in whatever direction a body moves on the earth's 

 surface there is a force arising from the earth's rotation which 

 tends to deflect it to the right in the northern hemisphere, but 

 to the left in the southern." This was published in May, 1858, 

 six months before it was discussed, with the same result, in the 

 French Academy of Sciences. Space can not be given here to 

 show the great importance of this principle in meteorology, but 

 if the reader desires to follow it to its applications he should con- 

 sult the Treatise on the Winds, named above. As to the im- 

 portance of the principle, let any one attempt to explain the mo- 

 tions of the wind and the distribution of atmospheric pressures 

 without it, and he will soon see the service rendered to meteorology 

 by Ferrel in its introduction. The essential quality of this prin- 

 ciple may perhaps be briefly stated. 



The general conception of the theory of the winds refers them 

 to convectional movements, arising from the action of gravity on 

 parts of the atmosphere of different temperatures. According to 

 this, the poles, where the temperatures are low, should have high 

 pressures, and the occurrence of low pressures there has been a 

 stumbling-block to more than one writer on the subject ; indeed, 

 hardly an English text-book can be named that will lead the 

 student around this difiiculty. The consideration introduced by 

 Ferrel is to the effect that the actual distribution of pressure does 

 not depend only on differences of temperature, but also on the 

 motions excited by reason of the pressure differences. The condi- 

 tion of steady motion, under which the winds are impelled by an 



