Arctowski — Pleionian Cycle of Climatic Flucttiations. 29 



Faculas are indeed merely a product of the solar atmospheric 

 circulation. Faculae occur often independently of sunspots, 

 but more often they accompany the spots. Some connection 

 exists also between the frequency of spots and the formation 

 of faculae. When sunspots are numerous, larger areas of the 

 solar surface are occupied by faculae. For the average charac- 

 teristic outbursts of sunspots, the accompanying faculae reach 

 their maximal development about nine days after the spotted- 

 ness has reached its maximum.* The faculae are evidently 

 one of the phases of the phenomenon that produces the 

 formation of spots. 



Admitting that a sunspot is the center of violent descending 

 currents in the solar atmosphere, we must admit that the 

 vapors slide sidewise from the spot when they reach the lower 

 levels and reascend, at a certain distance from the spot, more 

 quietly and overheated. It is to these ascending currents that 

 the formation of faculae must be ascribed. Faculae must, 

 therefore, radiate into space a quantity of heat larger than the 

 quantity of heat radiated by the spotted area. If so, the ratio 

 of the surfaces occupied by faculae and sunspots must equal or 

 be proportional to the ratio of radiation. 



If, therefore, the pleionian cycle of terrestrial temperature is 

 to be ascribed to solar fluctuations, we may presume that 

 the quotient of the areas of faculae and sunspots is not con- 

 stant, and we may suppose that the changes of this quotient 

 vary in harmony with the pleionian cycle. And the fact is, 

 that not only this ratio of faculae and spots varies extensively, 

 but also that these variations present some striking similarities 

 with the Arequipa or standard type of thermo-pleionian fluctua- 

 tions. 



The figures I have utilizedf are those of the Greenwich 

 photo-heliographic measurements. In order to eliminate the 

 shorter fluctuations, and to obtain numbers comparable to 

 annual means of temperature, I have formed the totals of the 

 areas of umbrae and faculae for every consecutive solar 10 

 rotations. I have used the figures given for the rotations 275 

 to 805, or the results of the measurements made during the 

 years 1875 to 1913. Then I divided the faculae numbers by 

 those for umbrae. The quotients thus obtained express numeri- 

 cally how many times the areas of faculae exceeded those of 

 umbrae. The curve representing these figures graphically, com- 

 pared with the curve of sunspots, shows an unmistakable cor- 

 relation with the 11-year period. The curve may indeed be 

 characterized as follows : 



*Mem. Soc. Spettr. Ital., Ser. II, vol. iv, p. 181, 1915. 

 flbid., p. 185, 1915. 



