WINDS OF THE NORTHEEN HEMISPHERE. 9 



only stations from which I have been able to obtain observations, are the few 

 marked on Plate I. in Hindoostan, though other collections, taken at Aden, in 

 Arabia, at Singapore, and at several other stations in Hindoostan, are known to 

 exist. 



Our information in regard to the winds of Africa, is confined to a few stations on 

 the northern and western borders, embracing in the aggregate a period of only 

 eleven months. I am aware of no series of observations ever taken in the interior, 

 except for three months only by the Niger expedition, and that still remains 

 unpublished, I believe, in the possession of the Koyal Society of London. The 

 series taken by Mr. Aime, at Algiers, and by Mr. Lambert, at Cairo, must be 

 valuable, but I have not been able to obtain them. 



There is reason to believe that most of the observations which form the basis of 

 this memoir, were taken with such accuracy that reliance may be safely placed on 

 the results, though there is, doubtless, considerable difference among them in this 

 respect. At nearly every station, the direction of the wind was recorded for at 

 least eight points of compass; at many, for sixteen points or more, together with 

 estimates of the force ; and at several,-^ either the direction, or force, or both, were 

 accurately measured and recorded by means of self-registering anemometers. 



The method of applying these data to determine the meaii direction of the wind 

 consists, as has already been remarked, not simply in finding from what point of 

 compass it has blown most frequently, and rejecting all the rest, but in resolving 

 the traverse of all the different courses. A ship at sea, having sailed on different 

 tacks, would find itself sadly out of its reckoning, if it were to take into account 

 merely the tack upon which it had sailed most frequently, or for the longest time. 

 The same would be the case if a balloon Avere set afloat in the air, and we wished to 

 know its course and distance after a given time, which is what is intended by the terms 

 mean direction and rate of progress, or percentage of resultant, as used in this memoir. 

 May not the imperfect manner in which the subject has generally been studied, 

 account for the belief so commonly entertained, that the winds in the temjjerate 

 zones are subject to no fixed laws; the prevailing direction being so dependent 

 upon the local features of the surrounding country, as often to furnish next to no 

 indication of the direction in which the air as a whole moves ? In any well-defined 

 valley of considerable extent, it is a familiar fact that the winds incline to take 

 the direction of the valley, marked examples of which the reader may see in the 

 stations on Hudson River, in the State of New York, as exhibited in Plate III. 

 Half the winds, or more, follow the course of the river, either up or down, and yet 

 the mean direction of the whole is nearly at right angles to it. 



The questions already enumerated will serve as a general index to the plan of 

 the work. It consists mainly of tabular statements, the difierent series being 

 designated by the capital letters. A, B, C, &c. 



* Toronto, Ogdensburg, and Girard College, on this continent; probably the three stations in Boothia 

 Felix; and Greenwich, Devonport, and Sturbington, in England. 



