694 THE POPULAR SCIENCE MONTHLY'. 



acceleration just sufficient to overcome their resistances, requires 

 that the acceleration should be not only the small component of 

 gravity acting on the barometric gradient, but the much smaller 

 resultant of this component acting with the deflective force aris- 

 ing from the motion of the wind itself. The course adopted by 

 the established interchanging circulation between the equator and 

 the poles consists for the most part of a great circumpolar whirl 

 from west to east ; and the deflective forces here in play reduce 

 the polar high pressures to low pressures. A reactionary relation 

 therefore exists between the winds and the pressures, by which the 

 distribution of pressures according to temperature alone is greatly 

 modified. Instead of finding high pressure at the cold poles, a low 

 pressure is produced there by the great circumpolar whirl of the 

 general winds, and the air thus held away from the poles accumu- 

 lates around the tropical belts of high pressure, of which Ferrel 

 had first learned from Maury's book. The absence of northeast re- 

 turn currents (in this hemisphere), except in the trade-wind belt, 

 is as important a feature of Ferrel's theory as the reversal of polar 

 high pressure into low pressure. Maury's erroneous explanation 

 of the winds gained great acceptance from the attractive style in 

 which his book was written ; but it is time that his explanation 

 should be abandoned even in elementary teaching, and replaced 

 by more serious views, less easily acquired but of more permanent 

 value. 



Ferrel's theory of the winds not only explains the general dis- 

 tribution of atmospheric pressure over the world, as no other 

 theory can do ; it introduces broad correlations among many phe- 

 nomena in meteorology, greatly to the advance of the science. 

 The legitimate analogies that may be drawn between the great 

 circumpolar whirl of the terrestrial winds, the smaller whirls of 

 tropical cyclones, and the concentrated whirling of tornadoes show 

 the unity of action of the convectional processes in the moist at- 

 mosphere of a rotating planet. In earlier years, meteorology con- 

 sisted chiefly of rules for observation and statistical study. The 

 broad generalizations taught by Ferrel raise the science from this 

 simple inductive condition and complete the philosophical round- 

 ing of its parts. 



Ferrel was not an observer, but he carefully based his studies 

 on well-ascertained facts. He was not an experimenter, but he 

 followed the results obtained by the best physicists. He was a 

 reasoner, able to employ the stronger methods of mathematical 

 analysis. He was sincere and judicial, single-minded and simple- 

 hearted. No one criticised his results more carefully or deliber- 

 ately than he did himself. He was indifferent to popularity, and 

 took little trouble to enforce his views on the world. He lived a 

 quiet life, more with books than with men, although the few to 



