The Solar Activity .1833-1900. 



293 



previously described. Special attention is called to the slow fall from 

 1843 to the minimum at 1867*2, and the rapid rise to 1879*0. 



It may be remarked that the value for the total spotted area for the 

 period 1833*9 to 1843*5, the earliest value in point of time dealt with, 

 is not quite in harmony with the other values. It is probable that 

 although at this period the time of maximum and minimum could be 

 accurately determined, the values may be too small owing to the fact 

 that Schwabe's observations were not made at that period quite on a 

 uniform plan. Mr. Warren de la Rue and Professor Balfour Stewart* 

 on this point wrote : — 



"By the commencement of 1832 Schwabe had matured his system 

 to such an extent as to give, no doubt with considerable precision, the 

 shape and area of each group ; although it was not until the commence- 

 ment of 1840 that he finally fixed upon the system of delineation, 

 which he henceforth pursued up to the time when he discontinued his 

 observations." 



The above suggestion seems to be borne out by the reduction of 

 sunspot photographs secured at the Wilna Observatory, where it was 

 found that the maximum of 1870 was of about the same order as that 

 of 1836. The Eeport of the Wilna Observatory for the year 1871 

 refers to this point in the following termsf : — 



" The curve traced from our observations about the last maximum 

 period of spots (1870) is one and a-half times as high as that of the 

 three most recent periods, i.e., the total sum of the areas of the spots 

 about the maximum period of 1870 was one and a-half times larger 

 than during the last thirty-six years.. This marked difference obliged 

 us to enter upon a double verification of our calculations, but we did 

 not discover any appreciable errors." 



With reference to the value given in the last line of the last column 

 of the table, although this is probably very near the truth, it is yet 

 impossible to state the date of the present minimum (1901*2 probably). 

 All the areas recorded since the minimum of 1890 and up to the 

 beginning of 1900 have been employed; this value is, however, 

 only slightly below the real one, so that a + sign has been printed 

 against it. 



If, therefore, these two facts be kept in mind, it will be seen that the 

 inverted total sunspot-area curve can be considered practically an exact 

 counterpart of the other two curves. 



The Total Area of the Magnetic Curves. From Minimum to Minimum. 



The remarkable similarity between the magnetic and sunspot curves, 

 especially in the later years when such observations are naturally more 



* 'Report of the Committee on Solar Physics, 1882.' Appendix. B, p. 77. 

 f Ibid., Appendix D, p. 154. 



