296 



Dr. W. J. S. Lockyer. 



minimum distinct features of the curve, but the periods (reckonino- 

 from minimum) vary slightly in length in the course of many mean 

 periods. More important still, the time of occurrence of the maximum 

 in relation to the preceding minimum varies to a comparatively large 

 extent in the course of few mean periods. The facts arranged in 

 tabular form sum up the information with regard both to the sunspot 

 curve and that of 77 Aquilas. 



To facilitate the comparison, the different intervals of time con- 

 verted into fractions and multiples of the sunspot (Q) and r\ Aquila? 

 (P) periods are given in separate columns. 







Light curve of 







Sun. 



7] Aquilae. 



Minimum to 

 minimum. 



Mean value 



Period of variation 

 Maximum variation 



Years. 

 11-20 

 Unknown 



± >1'4 



= Q 

 ? 



± > -12 Q, 



7d 4 h 14 m 4 



±3* 



= P 

 2400 P 



-017 P 



r 





Minimum to 

 maximum. 





4 -12 (about) 

 34 -8 „ 



±0-8 „ 



0-37Q 

 3-10Q 



±0-07Q 



2 d 5 



0-31 P 

 400 P 



±0-03 P 



Period of variation 

 Maximum variation 



± 5 h 





Fig. 3 is a reproduction of a set of light curves of the star 

 v) Aquilae, in which the dotted line and the two vertical wavy and 

 oblique dotted lines passing through the points of maxima and minima 

 indicate the variations of the times of maxima and minima. 



The curve for each group is the result of a combination of the obser- 

 vations made over a period equal in length to 100 mean periods (mean 

 period = I72 ll *2344) of the star. This whole set of curves is the 

 result of a discussion which I made of all the observations of 77 Aquilae 

 made by one observer, Herr Julius Schmidt. 



Other Cycles of about Thirty-five Years. 



Having found that, in addition to the well-known eleven-year period 

 of sunspot frequency, there is another cycle which extends over about 

 thirty-five years, and which is indicated clearly, as has been shown, 

 both by the changes in the times of the occurrence of the epochs of 

 maxima and in the variations in area included in consecutive eleven- 

 year periods of both sunspot and magnetic curves, it is only natural to 

 suppose that this long-period variation is the effect of a cycle of dis- 

 turbances in the Sun's atmosphere itself. 



