20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. ']'] 



The succeeding maps show that the areas of high and low pressure 

 thus formed in the western United States drift eastward and pass 

 ofif the eastern coast three days later. It is worthy of note that on 

 the day of the solar observation the high pressure accompanying 

 high values of solar radiation is found in the Rocky Mountain region 

 further west than the low pressure accompanying low values of solar 

 radiation, but as the areas of high and low pressure drift eastward 

 on subsequent days, the two come more nearly in opposition, so that 

 on the second and third days following the solar data (see figs. 13 

 to 16), the areas of high and low pressure on the maps following 

 high solar radiation are almost in exact opposition to the high and 

 low pressure areas following low solar radiation for the same 

 amounts of departure from normal radiation. Whether the differ- 

 ences in position found in the Rocky Mountain region on the day of 

 the solar observations are real differences, or merely due to variations 

 arising from other causes not eliminated in the means, remains for 

 the future to determine. 



In figures 17 and 18 are shown the mean departures from normal 

 pressure accompanying different intensities of solar radiation in 

 the summer half-year on the day of the solar observation. In 

 general, there is an intensification of the normal low pressure area 

 in the southern Rocky Mountain Plateau with high values of solar 

 radiation, and an increased pressure in the northern United States 

 and in southern Canada. With low values of solar radiation the 

 tendency is for the pressure to fall in the central and northern parts 

 of the United States and to rise in the south and east. This result 

 is not evident, however, in the case of the mean values below 1.911 

 calories, probably because of a lack of a sufficient number of obser- 

 vations. 



The charts for the succeeding days are not reproduced, but the 

 mean pressures are given in table 7 and can easily be plotted by 

 anyone wishing to study them. 



