NO. 3 SOLAR RADIATION AND THE WEATHER CLAYTON 33 



In obtaining the results given under " Third Method " the means 

 of nine periods were obtained and a " periodogram " made. From 

 the maximum amplitudes were read the corresponding lengths of the 

 periods and the mean amplitudes. This was the only method used 

 for determining the amplitude, as no satisfactory formula was found 

 for the first two cases. This method does not permit of determining 

 the length of the longer periods for lack of sufficient number of 

 periods. The true length and the amplitude of the period are given 

 under the heading " Real Periods." 



The estimated azimuth at the time of the epoch, or beginning of 

 each series, was read from the various plots and is given in columns 

 5 and 6, table X, followed by the true azimuths in column 7. 



The results from the second method were read from each plot by 

 me and are given in table XL This table shows clearly how assumed 

 periods near the true period enable the length of the different periods 

 to be estimated and how the means of successive estimates from 

 assumed periods of successively greater lengths allow the true periods 

 to be determined. 



The data in this table were obtained by plotting the phase angles 

 and amplitudes determined from the harmonic analysis of assumed 

 periods of successively greater length, indicating in the plots the 

 phase angles corresponding to the stronger amplitudes or beats, and 

 drawing straight lines through the indicated phase angles. Each 

 phase angle corresponding to a maximum beat was supposed to be 

 common to two periods and in the case of the extreme amplitude was 

 supposed to be common to three or more periods (see figure 10). 



Table XII shows the results of an analysis of the pressure at 

 Buenos Aires in periods of successively greater length using the 

 observed values of the pressure at 8 A. M. and 8 P. M. in July, 

 August, September, and October, 191 7. 



These results indicate a complex set of periods ; but when formed 

 in series, as shown at the bottom of the table, the shorter periods are 

 seen to be approximate submultiples of the longer periods. 



The temperatures observed at 8 A. M. and 8 P. M. each day at the 

 Observatory of Chacarita, Buenos Aires, were analysed in this way 

 for the years 1917 and 1918, using in the analysis, not only periods of 

 successively greater length in days and half-days to 30 days, but also 

 submultiples of a few longer periods. The frequencies of estimated 

 true periods were counted for short intervals, the intervals being 

 proportional to the length of the periods. Means were not taken, but 

 each estimated length was used in counting frequency of occurrence. 



