NO. 7 



THE ATMOSPHERE AND THE SUN CLAYTON 



31 



Figure 21 shows the observed values of solar radiation during 

 December, 1923. and January and February, 1924. These values are 

 compared with the observed values of pressure at Spitzbergen and 

 at Hamburg. A 24-day period of oscillation is evident in each case 

 and this oscillation is shown by the dotted curves computed from 

 the data in each case by harmonic analysis. Pressure data from all 



Fig. 21. — 24-day period in solar radiation and pressure. 



over the northern hemisphere were treated in this way for a period 

 of 24 days by Dr. Weickmann and showed a systematic wave 

 movement from the polar basin southward. 



For the study of long periods, no values of solar radiation are avail- 

 able; but the 7.5-year period shows a distinct relation to sun-spot 

 changes. Figure 22 shows a plot of consecutive means of three 

 periods of 7.5 years. This period is one-third of Hale's sun-spot 

 period of 22.5 years, and the mean of the three periods eliminates 

 the 11.3-year sun-spot period which is one-half of Hale's period. 



