PROFESSOR A. SCHUSTER ON THE PERIODICITIES OF SUNSPOTS. 
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The general character of the 11-year cycle not coming out with sufficient clearness 
when only annual averages are taken into account, I have deduced a more detailed 
curve (fig. 5), basing the calculation on the mean areas obtained during four 
successive rotations. We notice the sharp rise from the minimum, which takes place 
about 3^ years before the maximum elevation is reached. The maximum here shows 
three distinct peaks, and although their position may vary in the individual maxima, 
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the sharp secondary rise and fall of the activity in the time immediately following a 
maximum is characteristic. The temporary recovery of activity about 3 years after 
the maximum is also a feature which may often be traced in the separate cycles. 
I have investigated the sub-periods as well as the main 11-year period, taking 
the measurement of areas (publication b) as basis. Table XII. gives the results. It 
will be noted how closely the phase of the main period agrees with that derived in 
§ 4 from Wolf’s numbers. 
