A HISTORY OF SCIENCE 



be known as perhaps the foremost meteorologist of his 

 generation, included the winds among the subjects of 

 his elaborate statistical studies in climatology. 



Dove classified the winds as permanent, periodical, 

 and variable. His great discovery was that all winds, 

 of whatever character, and not merely the permanent 

 winds, come under the influence of the earth's rotation 

 in such a way as to be deflected from their course, and 

 hence to take on a gyratory motion that, in short, all 

 local winds are minor eddies in the great polar-equato- 

 rial whirl, and tend to reproduce in miniature the char- 

 acter of that vast maelstrom. For the first time, then, 

 temporary or variable winds were seen to lie within the 

 province of law. 



A generation later, Professor William Ferrel, the 

 American meteorologist, who had been led to take up 

 the subject by a perusal of Maury's discourse on ocean 

 winds, formulated a general mathematical law, to the 

 effect that any body moving in a right line along the 

 surface of the earth in any direction tends to have its 

 course deflected, owing to the earth's rotation, to the 

 right hand in the northern and to the left hand in 

 the southern hemisphere. This law had indeed been 

 stated as early as 1835 by the French physicist Poisson, 

 but no one then thought of it as other than a mathe- 

 matical curiosity; its true significance was only under- 

 stood after Professor Ferrel had independently redis- 

 covered it (just as Dalton rediscovered Hadley's for- 

 gotten law of the trade-winds) and applied it to the 

 motion of wind currents. 



Then it became clear that here is a key to the phe- 

 nomena of atmospheric circulation, from the great 



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