PREFACE. 



ill pointing out local peculiarities in the winds at diflferent places, as affected by 

 the geographical features of the surrounding country, but can give us no enlarged 

 ideas of the movement of the air as a whole.' Suppose a particle of air to start 

 from the point A, in the following diagram, and to move with a uniform velocity 

 for 30 days as foUovt^s : — 



From the northeast for an aggregate period of 3 days 



southeast 



south 



southwest 



west 



northwest 



the diagram represents its motions, and at the end of the 30 days the particle is 

 found at B. The bearing of the point 

 A from it is now S. 70° 4' W., its dis- 

 tance in a direct line equivalent to 12 

 days' travel, and the ratio of this dis- 

 tance to the whole distance travelled 

 40 per cent. 



" Or, to express the same by formulae 

 after the method of Lambert, or of 

 Mr. Charles A. Schott, of the United 

 States Coast Survey,^ or others, who 

 have improved upon Lambert's me- 

 thod, let n represent the total number 

 of observations (corresponding to the 

 sum of the sides of the foregoing polygon, except A B) ; 0, Oj, 02? ^3 • • • • • the 

 angles which the observed directions of the wind make with the meridian, reckoned 

 round the compass from the north point eastward through 360° ; /S', /S'l, /S'a, S^, . . 

 . . . the number of observations recorded in these directions (corresponding to the 

 foregoing sides taken separately); E. the resulting distance A B, and ^ the angle 



' The following is an extract from a letter of the author, in 1871, on this point: "The question as 

 to the proper mode of discussing winds depends on what we wish to ascertain or point out. If it be 

 to show their sanitary effect, or what winds one is likely to experience at any given place, Lambert's 

 formula is manifestly inadequate, nor was it designed for that purpose. But, if the object be to 

 ascertain in what direction the air, subject to observation, moves as a whole over a given place, it is 

 equally obvious that the only proper method is to resolve its traverse; and to abandon this method 

 would, in my view, put the science back a third of a century. It was the chaotic character of the 

 results that came from the method formerly in vogue, that first drew my attention to the subject, and 

 led me to conceive the idea of resolving the traverse of the winds : ignorant of Lambert's formula, as 

 well as of the fact that Prof. Kaemtz was doing the same thing. The soundness of the principle 

 seemed so obvious, and the results of its application so satisfactory, all over the globe, that I had 

 not supposed it possible that it could ever be called in question." 



^ See his reduction of Dr. Kane's Arctic observations, published in the Smithsonian Contribu- 

 tions to Knowledge, Vol. XI. 

 B August, 1875. 



