1871.] on some recent Researches in Solar Physics, 83 



minimum, and applying this method to five distinct minimum epochs, 

 which he has fixed for the following years : — 



1823-2 



1833-8 



1844-0 



1856-2 



1867-2 



3. In a Table he gives their mean numbers, expressing the solar activity, 

 arranged in various columns, and arrives at the following results : — 



(1) It is shown now, with greater precision than was previously pos- 

 sible, that the curve of sun-spots ascends with greater rapidity than it 

 descends. This fact is shown in the subjoined diagram, which it may be 

 of interest to compare with the curves given previously by ourselves in the 

 above-mentioned place. The zero-point in this diagram corresponds to 

 the minimum of each period ; the abscissae give the time before and after 

 it, viz. two and a half years, or thirty months ; the ordinates express the 

 amount of spot-production in numbers of an arbitrary scale. The two 

 finely dotted curves are intended to show the actual character of a portion 

 of two periods only, viz. those which had their minima in 1823*2 and 

 1867*2 ; the strongly dotted curve, however, gives the mean of all periods 

 (five) over which the investigation extends. 



(2) Denoting by x the number of years during which the curve ascen Is» 



