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ciency, while a small range is accompanied with a depression 
of the same. The result is a curve of the base line of which 
the period is roughly speaking eleven years. May we not 
therefore imagine that the so-called eleven-yearly period or, 
to speak more correctly, the ten and a half and twelve- 
yearly periods into which the eleven-yearly period may 
perhaps be analysed, may be in reality bent periods for 
shorter disturbances ? Is it not therefore possible that a 
study of these shorter periods may give us information 
regarding the nature of the eleven-yearly period, whether 
for sun spots or declination ranges, which the small series of 
actual observations is incompetent to afford ? 
We beg to take this opportunity of thanking Mr. William 
Stroud for the help he has given us in this investigation. 
