July 29, i9?o] 



NATUHE 



679 



or months. Both types of variation are highly 

 irregular. The longer-period type appears to 

 reach 4 per cent, for 100 Wolf sun-spot numbers. 

 The shorter-period . changes are larger, and 

 often amount to 3 or even 5 per cent, in a 

 week or a fortnight. Sometimes they reach 

 10 per cent. 



In order to test the validity of these apparent 

 solar changes, we secured nearly simultaneous 

 observations at Washington (sea-level) and Mount 

 Wilson (1730 metres). Also in 1909 and 1910 at 

 Mount Wilson and Mount Whitney (4440 metres) 

 close agreement of results was found. Then in 

 191 1 and 1912 we observed nearly simultaneously 

 for several months at both Mount Wilson and 

 Bassour, Algeria (1160 metres). Both Mount 

 Wilson and Bassour indicated a range cf solar 

 variation of nearly 10 per cent. The coefficient of 

 correlation betv.cen their indica- 

 tions in 1912, according to Mr. 

 Knox Shaw's determination, is 

 -f 58 + 79 per cent. Thus our view 

 of the sun's short-period irregular 

 variation was confirmed by the 

 agreement of these results from 

 two stations separated by one- 

 third of the earth's circum- 

 ference. 



Since then we have confirmed 

 the solar variability in many 

 ways. Most convincing, perhaps, 

 is the variation we have found in 

 the distribution of radiation over 

 the sun's disc attending changes 

 in the solar radiation. As is well 

 known, the sun's centre is 

 brighter than its edges. We find 

 that the contrast of centre to edge 

 changes from day to day and from 

 year to year. These twofold 

 changes run in opposite Senses 

 with respect to increased solar 

 radiation, and seem to indicate 

 that the cause of the solar varia- 

 tion of long period is the hottei 

 sun attending increased circula- 

 tion at sun-spot maximum, while the short-interval 

 changes are caused by changes of transparency of 

 the sun's outer layers. 



In 1918 the Smithsonian Institution established 

 a station at Calama, Chile, supposed to be one 

 of the earth's most cloudless regions. We have 

 been disappointed in the degree of cloudlessness, 



but our young men have observed the " solar con- 

 stant " there on about 75 per cent, of all days 

 since July 27, 1918. Comparisons with Mount 

 Wilson in 1918 f>-ave a "probable error" for one 

 determination at a single station of 001 11 calorie, 

 or about 06 per cent. The Calama values have 

 ranged from 1884 to 2028 calories, or 7 per 

 cent. 



Mr. H. H. Clayton, chief forecaster of the 

 Arp^entine Meteorological Service, has compared 

 all the Mount Wilson and Calama solar observa- 

 tions, 1905 to 1920 inclusive, with the tempera- 

 tures and rainfall of Argentina. He finds a high 

 degree of correlation between them. The sub- 

 joined table shows Clayton's comparison of the 

 average marches of temperature in Buenos Aires 

 for the years 1913, 1914, 1915, and 1918 (1916 

 and 191 7 were not available to him), correspond- 



Q 2 4 6 6 iO J2 H /6 v ^0 

 U/ys Et^apsej) ATTLn Sola n Op^cnvA-r-r^i'- ® 



,._The prolonged influence of solar changes on terrestrial temperatures. The three curves 

 show the average march of temperature departures at Buenos Aires, as published by Mr. H. H. 

 Clayton, for nineteen days next following days of maximum, mean, and minimum solar radiation 

 in the years lyn, 1914, 1915, and 1918 for the months May to November. The solar 

 o1.»ervations were made by the Smithsonian Astrophyiical Observatory at Mount Wilson,^ 

 California, more than six thousand miles from Buenos Aires. The curves marked " Max.," 

 " Mean," and "Min." correspond respectively to mean values of the "solar constant" of a'oo, 

 I '05, and fgo calories per square centimetre per minute. 



ing to all the occasions when the solar constant 

 values observed at Mount Wilson fell between 

 the stated limits. The deviations of temperature 

 are expressed in tenths of degrees Centigrade, 

 and range from -f2.o° to -i-5° C. from the 

 normal. The extreme and mean results are given 

 also, translated into Fahrenheit, in Fig. i. 



Derivations from Normal Temperature in Buenos Aires following Different Intensities of Solar 



Radiation (May to November). 



Solar radiation 

 values in gram- 

 caloriespercm.2 



per min. o 



2'0OO + O 010 - 12 



i-qSo+o-oio - I 



i-96o±o-oio 2 



I'040 + O'OIO 2 



I •920+0010 9 



i'90o±c*dio 10 



Days following 



-7 

 -6 



-5 



-2 



4 



I 



-4 



23 



-7 

 -8 



-2 



9 



-6 



-9 



- 2 

 o 



- 2 

 2 



- 4 

 -10 



2 

 - 9 



7 

 3 

 9 

 o 

 o 

 -5 



-10 - 15 



8 

 15 



9 



-2 



-3 



-2 

 -8 



20 

 S 



- 4 



- 3 

 3 



-14 



14 



4 



-5 



7 



3 



-5 



12 13 



- 1 I 



7 9 



-I -4 



2 -5 



5 6 



I -3 



2 

 S 



-s 

 -s 



3 



IS 



6 

 - 1 

 - 1 

 -6 



-s 



16 

 8 



2 

 -2 

 -3 

 -3 



■3 -13 



NO. 2648, VOL. 105] 



