NO. 6 SOLAR RADIATION AND WEATHER CLAYTON 45 



The observations of solar radiation from 192 1 to 1924 were selected 

 for more detailed study, first because the solar radiation data were 

 more complete and accurate during this period, and second because 

 the spots were less frequent and there was less confusion from the 

 overlapping of the effects of succeeding groups of spots. The data 

 were tabulated in the manner previously explained after separation 

 into several dififerent classes ; first into large spots and small spots, 

 then into groups of spots and single spots, then into spots increasing 

 in size and decreasing in size, and finally into spots north of the 

 equator and south of the equator. The mean radiation for these 

 different classes is shown in table 13. 



Figures 36 and 37 show plots of these means. The mean radiation 

 following large spots and small spots, plotted in figure 36, shows 

 the same general trend in each case, the cooler side of the sun being 

 on the side with the spots, but the lesser maxima, A, B, etc., are not 

 distinctly marked in the case of the smaller spots. 



In the lower part of figure 36 is plotted the mean solar radiation 

 attending groups of spots and single spots. Here the two sets of 

 mean values are very similar and show that any difference in the 

 solar effect is due to difference in size and not to differences in 

 grouping. Figure 37 shows a plot of the division into classes of 

 spots increasing and decreasing in size, and of spots 10° or more 

 north of the equator and 10° or more south of the equator. The 

 number of cases was not great enough to form very trustworthy 

 means, but in the case of spots increasing and decreasing in size, 

 the only difference appears to be that with increasing spots the 

 general trend of the mean radiation is downward and with decreasing 

 spots is upward, as shown by the differences at the beginning and 

 end of the period. In the case of spots north and south of the 

 equator the details of the plots are different, probably because of 

 insufficient observations, but the general trend shown by the broken 

 curve is the same in both cases. 



Next the temperature and pressure at selected stations in the 

 United States were averaged in relation to the position of sun spots. 



In table 14 the mean pressure and temperature attending the 

 passage of large spots across the sun is given for Winnipeg and 

 New York, for the interval from 7 days before to 22 days after the 

 passage of the spots across the central meridian as seen from the 

 earth, using all large spots observed from January, 192 1, to July, 1924. 

 The number of cases is 41. The results are plotted in figure 38. The 

 first half of the diagram, on the left, shows the changes in the mean 



