444 WRITINGS OF JOSEPH HENRY. [1861 



within the tropics, there is a belt along which the wind con- 

 stantly blows from an easterly direction; and from the com- 

 bined meteorological observations made in different parts of 

 the world within the last few years, that north of this belt, 

 between the latitudes of 30° and 60° around the whole 

 earth, the resultant wind is from a westerly direction. 



The primary motive power which gives rise to these cur- 

 rents is the constant heating of the air in the equatorial, 

 and the cooling of it in and toward the polar regions ; the 

 eastern and western deflections of these currents being due 

 to the rotation of the earth on its axis. 



The easterly currents in the equatorial regions are always 

 at the surface and have long been known as the trade winds, 

 while the currents from the west are constantly flowing in the 

 upper portion of the atmosphere, and only reach the sur- 

 face of the earth at intervals, — generally after the occurrence 

 of a storm. 



Although the wind (at the surface) over the United States 

 and around the whole earth between the same parallels, 

 appears to be exceedingly fitful, yet when the average move- 

 ment is accurately recorded for a number of years, it is found 

 that there remains a large resultant of a westerl}^ current. 

 This is well established by the fact that on an average of 

 many years packet ships sailing between New York and 

 Great Britain occupy nearly double the time in returning 

 that they do in going. 



It has been fully established by continuous observations 

 for ten years collected at this Institution from every part of 

 the United States, that as a general rule all the meteorologi- 

 cal phenomena advance from west to east, and that the 

 higher clouds always move eastwardly. We are therefore 

 from abundant observations as well as from theoretical con- 

 siderations, enabled to state with confidence that on a given 

 day, whatever may be the direction of the wind at the sur- 

 face of the earth, a balloon elevated sufficiently high would 

 be carried eastwardl}' by the prevailing current in the upper 

 or rather middle region of the atmosphere. 



I do not hesitate therefore to say that provided a bal- 



