30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. // 



month is obtained with solar radiation 0.5 per cent above normal. 

 In this way there is formed a series showing the positions of the 

 areas of departures from normal with different intensities of solar 

 radiation of 0.5 per cent running from i per cent above to i per cent 

 below normal, with only one step missing. Figure 20 shows the 

 departures of pressure from normal over the Xorth American con- 

 tinent in January, 1920, when the solar radiation was i per cent 

 above normal. It is seen that a marked excess of pressure is found 

 in Alaska and northern Canada, with the maximum departures near 

 the 6oth parallel of latitude. In February (see fig. 22) with a 

 decrease of 0.5 per cent in the mean solar radiation, the excess of 

 pressure is displaced southward and the maximum is found near the 

 latitude of 52° N. In January, 1919 (see fig. 24), the solar radiation 

 was normal or 0.5 per cent lower than in February, 1920, and the 

 maximum excess of pressure is found in the Rocky [Mountain region 

 near the latitude of 40° X. This is near the normal position of the 

 high pressure area in the United States which is thus shown to be 

 intensified when the solar radiation is normal, as is also the low 

 pressure which is found in the vicinity of Alaska. Figure 26 shows 

 the distribution of pressure in January, 1923, when the solar radiation 

 was I per cent below normal. The excess of pressure is now displaced 

 southward to near the latitude of 30° N.. and a defect of pressure 

 covers the larger part of the United States and Alaska, so that the 

 distribution is nearly opposite to that in January, 1920, when the 

 solar radiation was i per cent above normal. It should be noted 

 also that the greatest defect of pressure in Canada is displaced 

 southward of its position in 1919 some 10° or more. 



The departures of temperature from normal are found closely 

 related to the departures of pressure and change their positions in 

 unison with them. By comparing the charts of pressure and of tem- 

 perature departures, figures 20 to 2"], it is seen that the warm areas 

 are north of the maximum excess of pressure and south of the 

 maximum defect of pressure, while the areas of cold are south or 

 southeast of the areas of excehs pressure and north or west of the 

 areas of deficient pressure. 



Figure 21 shows the departures from normal temperature in Xorth 

 America in January, 1920, when the solar radiation averaged i per 

 cent above normal. An area of cold covers all of Canada and a 

 large part of the United States with the area of greatest departure 

 in the St. Lawrence Valley, where the temperature averages from 

 9° F. to 13° F. below n^ormal. There was an area of slight excess in 



