The Solar Activity 1833-1900. 295 



Minimum 



Sunspots. 



Magnetics. 



Combination. 



beginning 

 in the 

 year 



Minimum 

 to 



minimum. 



Differences 

 from 

 mean. 



Minimum 

 to 



minimum. 



Differences 

 from 

 mean. 



Minimum 

 to 



minimum. 

 t 



Differences 

 from 

 mean. 



1833-. 



1843 J -, 



1856-J 



1867 J -i 



1879-,-! 



1890^ 



Years. 



9'6 

 12 -5 

 11-2 

 11-8 

 11-2 



Years. 



-1-7 

 + 1-2 

 -O'l 

 + 0'5 

 -O'l 



Years. 



12 : 55 

 11 -40 

 11-30 

 10-90 



Years. 



+ 1-0 

 -0-14 

 -0'24 

 -0-64 



Years. 



9-6 

 12 -52 

 11 -30 

 11 -55 

 11 -05 



Years. 



-1-7 

 + 1-32 

 + 0-10 

 + 0-35 

 -0-15 



Means . . 



11 3 





11 -54 





11 -20 





Although there is a suspected variation in the length of both the 

 magnetic and sunspot periods (reckoning from minimum to minimum), 

 which increases and decreases in alternate eleven-year periods from 

 a mean value, the observations do not extend over a sufficient interval 

 of time to allow a more definite conclusion to be drawn. 



Relation of the Sunspot Curve to the Light Curve of 7) Aquilce. 



It is generally conceded that the spots on the surface of the Sun are 

 the result of greater activity in the circulation in the solar atmosphere, 

 and therefore indicate greater heat and, therefore, light. This being 

 so, the carve representing the spotted area may be regarded as a light 

 curve of the Sun. 



The Sun may thus be considered a variable star (1) the light of 

 which (reckoning from minimum to minimum) is variable, with a mean 

 value of about 11*1 years ; (2) the epoch of maximum does not occur 

 a constant number of years after the preceding minimum, but varies 

 regularly, the cycle of variations covering about 35 years. 



It is interesting therefore to inquire whether there be any other 

 known star or stars which exhibit variations similar in kind to those 

 given above. 



In the year 18% I undertook the investigation of all the observa- 

 tions, whether published or not, of the variable star rj Aquilse * which 

 had been made between the years 1840 to 1891, numbering in all 

 12,000. 



For the present inquiry the light curve of this star is of great 

 interest, as its chief peculiarities are similar to those I have indicated 

 in connection with the sunspot curve. 



Not only are the more rapid rise to maximum and slow fall to 



* ' Eesultate aus den Beobachtungen des veranderlichen Sternes rj Aquilte,' 

 Inaugural-Dissertation, Universit. Grottingen, 1897 (Dulau and Co., London). 



