410 Eighth Annual Report of the 



From this table it will be seen that the westerly winds from 

 the interior of America give the northeastern States about the 

 &j\me mid-winter temperature which prevails in western Europe 

 at the arctic circle, while at our latitude the mid-summer heat of 

 the two coasts is nearly equal on the same parallels. In general, 

 north of latitude 40 degrees the annual temperature of land sur- 

 faces is less than that of the oceans. 



A more detailed account of the character and climatic effect 

 of prevailing winds requires some consideration of the distribu- 

 tion of atmosphei4c pressure. Air masses are forced out from 

 regions of high toward those of low barometer, and, owing to a 

 deflecting force due to the eanth's rotation, these outflowing 

 winds in the No^rthern Hemisphere also tend to circulate about 

 the center of high pressure in the direction in which the hands 

 of a watch move. The winds flowing toward a center of low 

 pressure revolve about it in a direction opposite to the move- 

 ments of watch hands. 



The principal permanent high pressure system to be consid- 

 ered in connection with our own climate is the vast area stretch- 

 ing across the Atlantic between latitude® 20 and 40 degrees, 

 moving somewhat northward from the average position in sum- 

 mer and autumn and to the south of it in winter. This area 

 forms part of a belt of high mean pressure which extends around 

 the globe near latitude 30 degrees north. 



A permanent area of low barometer is found over the north 

 Atlantic, with a minimum pressure of 29.5 inches to the east of 

 Greenland in January. The depression is much less intense 

 during the summer, but nevertheless controls the winds of the 

 northern Atlantic and northeastern America throughout the 

 greater portion of the year. 



Thirdly, the intense winter cold of the land surfaces in the 

 interior of the continent causes a oontraction of the lower air 

 strata and consequently an inflow at higher levels from surround- 

 ing warmer regions. Thus the maiss of air becomes greater 

 over the cold area and the barometric pressure increases. In 

 Bummer the oceans become, relatively, cold areas, and hence a 



