84 
PROFESSOR A. SCHUSTER ON THE PERIODICITIES OF SUNSPOTS. 
consider the individual maxima at times when otherwise the sunspot activity is small. 
The maxima of December 4, 1855, December 23, 1879, and August 7, 1889, satisfy 
that condition. According to the records tabulated by the Solar Physics Committee, 
the sunspot activity between March 15, 1855, and July, 1856, was exceedingly small, 
rising above 30 (the unit is the millionth of the sun’s hemisphere) only in the two 
rotations beginning October 20 and November 16. During the latter rotation the 
area was 61. The only notable outbreak during 16 months, therefore, took place at 
a time closely coincident with the theoretical maximum. According to Carrington*s 
drawings the spots seen were close to the equator and in the northern hemisphere. 
At the end of 1879 the sunspot activity began to increase again towards the 
maximum, which took place five years afterwards. The first notable outbreak took 
place during the rotation which began on December 30, closely following the maximum 
of the period we are considering. 
The year 1889 was one of minimum activity, though spots were occasionally 
observed. The sunspot areas in the rotations beginning on July 21 were 345, the 
four preceding rotations gave 19, 17, 160, 214, and the four following ones 101, 
59, 2, 0. There was here, therefore, a very sharp outbreak during an otherwise 
quiescent time. The outbreak occurred in the Southern hemisphere. There are other 
equally marked signs of increased activity at times which are close to all the 
calculated maxima, except that of 1860. This year coincides with a general 
maximum at which the main and most powerful influence which causes the 11-year 
period must only be expected to overshadow the weaker periodicity. The year 1894 
was one in which the sunspot activity began to show a downward tendency. The 
most notable spots were noticed in the rotation beginning with May 29, the exact 
date of the calculated maximum of the period of 4'81 years. Here again the chief 
spots were in the Southern hemisphere. If we identify the outbreaks in the rotations 
beginning November 27, 1836, and March 10, 1899, with this particular period, the 
periodic time is found to be 4'79. 1 am inclined to think that the evidence of the 
more accurate observations in the last fifty years is in favour of a period somewhat 
less than 4"81, but further observations are needed to decide this point. Provisionally, 
I adopt 479 as the most probable time, and 190372+ 479n as the most probable 
date of future maxima. 
Table X. may serve to facilitate the further study of this period. It gives the 
sum of the sixteen columns containing the entries from which the periodicity was 
deduced. In the original table each entry represented the sum of the mean areas 
during four successive rotations, and the numbers given here are the sum of fourteen 
rows, each row corresponding to a period of 478 years. The central date of the 
first entry which fixes the epoch is March 15, 1832, or 1832-203. The amplitude and 
phase are calculated from the values of A = +41406 and B = -15249. The phase is 
found to be -20° 13', and this gives the date of the first maximum as - A°H 5 x 475, 
or 0767 years before the epoch, i.e., in 183P94. 
