WINDS 



NOETHEEN HEMISPHEEE 



The design of this memoir is to answer, as far as practicable, the following 

 questions, viz: — 



1. What is the mean direction in which the lower strata of the air move over 

 different portions of the Northern Hemisphere ; including in the term loioer strata 

 all that part of the atmosphere on which direct observations can be made, whether 

 by the motion of the clouds, or by means of a vane? 



2. What is the rate of progress in this mean direction, as compared with the 

 total distance travelled by the wind? 



3. What modifications does this mean direction, and rate of progress, undergo in 

 the different months of the year? 



4. What is the direction and amount of the deflecting forces that cause these 

 modifications ? 



5. What is the average relaiice velocity of winds from the several points of 

 compass ? 



6. How will the introduction or omission of this latter element affect the 

 answers to the preceding questions? 



The data which I use for elucidating the questions here proposed, consist of 

 series of observations on winds taken at nearly 600 different stations on land, and 

 during numerous voyages at sea, extending from the equator nearly to the parallel 

 of 83° of latitude (the most northerly point ever reached by man), and embracing 

 an aggregate period of over 2,800 years. Were these stations distributed uniformly 

 over the entire Northern Hemisphere, we should have about one in every 418 

 miles square, which would afford us tolerably fair data for the investigation. But, 

 unfortunately, this is not the case, as may be seen by inspecting Plate I., which 

 shows by dots their position. In the United States, and in several of the coun- 

 tries of Europe, the materials are abundant, and, through the operations of the 

 National Observatory, under the direction of Lieut. Maury, we have very satis- 



