REPORT OF THE SECRETARY. 23 



returning toward the equator, forming the trade-wind, and the other, 

 proceeding northward, having a westerly component by the revolution 

 of the earth, tends to move in a direction from the west. It is probable, 

 however, that a portion of the upper wind from the equator flows entirely 

 to the pole, and there, by cooling, descends, consequently having a north- 

 easterly direction. The point of union of these two currents produces 

 an upward motion, again giving rise to the northern belt of lower 

 barometer. 



This sketch of the direction of the wind at the surface of the earth is 

 shown by Professor Coffin to exist by deductions from actual observa- 

 tions, while it is also proved by Professor Ferrel, of the Coast Survey, 

 as a mathematical deduction from the theory of a fluid subjected to dif- 

 ference of temperatures at different parts on the surface of a rotating 

 globe. 



The material which Dr. Woeikof has supplied to this work consists 

 in an elaborate comparison of the actual winds, as tabulated from the 

 reductions of Professor Coffin, with the varying pressure of the atmos- 

 phere at different seasons of the year due to the relative variation of the 

 heat of the land and of the sea, on the principle adopted by Buchan. 

 The result of his labor gives a satisfactory account in all cases where 

 the pressure has been determined of the perturbations in the direction 

 and intensity of the wind in different seasons of the year; and is a val- 

 uable first approximation to a full analysis of the causes of the com- 

 plex phenomena of the local and periodical changes in the atmosphere. 



The results given in the tables of the whole world are represented and 

 illustrated by twenty-six plates drawn by Prof. S. J. Coffin, and en- 

 graved by Henry Chandler, of Buffalo, N. Y. These plates present, at 

 a single view, the relation of the different parts of the same system of 

 winds to each other and to the different systems of the globe. For the 

 illustration of the deductions of Dr„ Woeikof, two plates are reproduced 

 from the paper of Professor Buchan in the Transactions of the Royal 

 Society of Edinburgh. We trust this work will be accepted by the 

 scientific world as a monument to the memory of Professor Coffin, and 

 as an illustration of the judicious policy of the Smithsonian Institution. 



The extended series of tables relative to the Temperature of the 

 United States which has been in progress of preparation for a number 

 of years, is now nearly through the press, and will be ready for distri- 

 bution in the course of 1876. 



This memoir contains the results of all observations to the end of the 

 year 1870, from the following sources : 



1st. The registers of the Smithsonian Institution, embracing upward 

 of 300 folio volumes. 



2d. The joint publications of the Institution, the Patent-Office, and 

 the Department of Agriculture. 



3d. All the publications aud unpublished records of the meteorolog- 

 ical system of the United States Army. 



