PROFESSOR A. SCHUSTER ON THE PERIODICITIES OF SUNSPOTS. 
95 
Table XYI. 
Calculated 
Calculated 
Principal 
maximum. 
maximum. 
outbreaks. 
1870-7 
1835-7 
1836-9] 
1870-4 
1836-7 | 
1837-5 
1837-9 
1871-1 
1837-6 
1870-2] 
[1869-2] 
[1836-1] 
1870-4 
1870-4 
1837-0 
1870-7 
1872-0 
1870-0 
1838-6 
1 
1871-3 J 
[1871-4] 
/ ~ 
Period. 
4-38 
4-80 
8-36 
11-125 
13-5 
Of the two numbers given for the 11-year period the first refers to the observed 
maximum of the total oscillation which includes the harmonics, while the second gives 
the maximum phase of the fundamental period. The last column gives the dates of 
the principal outbreaks which together make up the two maxima concerned. 
The significance of the table may be thought to be weakened to some extent by 
the consideration that the two exceptional maxima of 1837 and 1870 make them¬ 
selves felt in the numerical reductions, tending to attract the maximum of any 
periodicity towards themselves. I have therefore for the two periods of 8'3 and 
13'5 years added in brackets the dates of the maxima calculated from observations 
which all were previous to 1826, and which could not be affected in this manner. 
17. The general conclusion arrived at brings us, I think, a decided step nearer to 
the solution of the problem of sunspot periodicities. The existence of a number of 
definite periods cannot be doubted, whatever we may think of their numerical 
relationship. The recurrence of the maximum activity of each period seems to take 
place with an accuracy which may be equal to that of orbital revolution, but the 
characteristic property of these periods is the great variability of the activity. To 
this variability we must attribute the cause why the periodicities have been allowed 
to remain hidden for so long a time. If we associate the periods, as seems natural, 
with the existence of meteor streams, these streams must vary in the power of 
setting up the disturbance which is the ultimate cause of the formation of a spot. 
I have for a long time believed in, and occasionally expressed, the opinion that sun¬ 
spots are only secondary phenomena consequent on disturbances in the immediate 
surroundings of the sun, which are due to a general increase of electric conductivity 
affecting a great portion of interplanetary space. Such change in electric conductivity 
could be brought about by meteoric swarms fertilised by ionized matter which they 
have picked up in their journey through space. 
The answer to many questions which naturally occur can only be given when further 
