NO. 10 SOLAR RADIATION AND WEATHER STUDIES ABBOT I9 



7 or 8 months. The fractional diminution produced thereby on the 

 amphtude of the 7-month periodicity is estimated to exceed one-half. 

 For the 8-month and 9|-month periodicities the effect is still con- 

 siderable, though smaller. For periodicities of 11 months or more it 

 is believed to be inconsiderable. No corresponding effects of diminu- 

 tion occur in the analysis of the solar-constant variation itself because 

 the solar data are not siiioothed by 5-month traveling means as are 

 the weather data. 



II. SuN-SPOT Data 



As indicated under caption 8, there was evidence to indicate that 

 changes of phase in weather periodicities occur when the activity of 

 the sun alters as measured by the Wolf sun-spot numbers. Therefore, 

 before entering upon statistical computations from weather data ex- 

 tending over the past century, the first step was to assign the be- 

 ginnings and ends of intervals throughout which sun-spot numbers 

 were approximately equal. To this end the monthly mean sun-spot 

 numbers given in " World Weather Records " were plotted as in 

 figure 10. In preparing figure 10, a 23-year arrangement of the sun- 

 spot data has been adopted. It will be noticed that, excepting the first 

 of the 23-year cycles shown, there is a very fair constancy of positions 

 of maxima and minima in the successive 23-year intervals. From this 

 plot the following intervals were selected as of comparable sun-spot 

 activity : 



(a) Sun-spot numbers generally below 40. 



Jan. i8ii-Aug. 1815; Aug. i8i8-Feb. 1826; Jan. 1832-Nov. 1834; 

 May 1841-Oct. 1844; Aug. 1853-Aug. 1857; Apr. 1865-Sept. 1868; 

 Aug. 1874-May 1880; Nov. 1889-June 1891 ; Dec. 1897-Sept. 1903; 

 Mar. 1910-Oct. 1914; June 1922-Apr. 1925. 



(b) Sun-spot numbers generally above 40 but below 80. 



(bi) Ascending values (or ascending and descending values con- 

 tiguous). Sept. i8iS-July 1818; Mar. 1826-Dec. 183 1 ; Dec. 1834- 

 July 1835; Nov. 1844-July 1846; Sept. 1857-Mar. 1865; Oct. 1868- 

 Apr. 1869; June 1880-Oct. 1886; July 1891-Jan. 1892; Oct. 1903- 

 Feb. 1910; Nov. 1914-Feb. 1917; May 1925-Dec. 1929. 



(ba) Descending values. Aug. 1839-Apr. 1841 ; July 1849-July 

 1853; Jan. 1873-July 1874; June 1894-Nov. 1897; July 1919-May 

 1922. 



(c) Sun-spot numbers generally above 80. 



Aug. 1835-Aug. 1839; Aug. 1846-June 1849; May 1869-May 

 1873; Feb. 1892-May 1894; Mar. 1917-June 1919. 



