228 } Original Articles. | April, 
years in which the solar activity fluctuates from nil, or nearly, so to a 
maximum and back again, it is subject to another and larger period of 
56 years (55°55 ?), during which the extent of the former fluctuation is 
nearly doubled. The maximum of this greater fluctuation may pro- 
visionally be placed about the years 1780 and 1836. 2nd. Another 
conclusion hardly less interesting is, that in adjacent or nearly adjacent 
11-year periods of unequal length, a greater degree of activity during 
the shorter tends to compensate in the total number of spots produced, 
for a less energy in the longer. 
These results are in a high degree enigmatical, and up to the 
present time no clear account of them has been given. Were the spots 
sufficiently large and numerous to produce any considerable defalcation 
of light they would place the sun at once in the class of variable stars, 
which present distinct and marked analogies in respect of their laws 
of periodicity and sub-periodicity, such as at all events point toa 
common explanation of the two phenomena. Meanwhile it must be 
noted that in the planetary revolutions we find no such periods as 112 
and 552 years, and although both Professors Wolf and Schmidt have 
bestowed some pains on the inquiry whether the application of equa- 
tions or terms depending on the heliocentric longitudes of the planets 
may not eliminate some portion of the observed irregularities in the 
recurrence of the minima of the 11-year period, it does not yet appear 
that any dependable result of this kind has been arrived at. Indeed, 
the data have not sufficient precision, nor does the series of observations 
embrace a sufficient time to lead us to expect it. 
As regards the number of spots in each year and in different 
months of the same year, however, Dr. Wolf (‘ Mittheilungen,’ No. X.) 
seems to have satisfied himself from the examination of Schwabe’s 
observations from 1826 to 1848 that sub-periods depending on the 
revolutions of the Earth and of Venus do really exist. Thus, he finds 
a perceptibly greater degree of apparent activity to prevail annually 
on the average of months of September..... January, than in the 
other months of each year—and again by projecting all the results in 
a continuous curve he finds in it a series of small undulations suc- 
ceeding each other at an average interval of 7°65 months, or 0°637 
year. Now the periodic time of Venus (225 days) reduced to a fraction 
of the year is 0°616, a coincidence certainly near enough to warrant 
some considerable suspicion of a physical connection. 
Yet more enigmatical is the connection which has been considered 
to subsist between the mean annual abundance of solar spots and the 
extent of mean annual fluctuation observable in the magnetic elements 
which determine the position of the needle. Dr. Lamont, of Munich, 
it would appear, was the first who noticed a periodical increase and 
decrease in the annual amount of variation of the magnetic declina- 
tion-—the period assigned by him being about ten years. In his 
‘Resultate der Mag. Obs. zu Miinchen,’ published in 1846, he states 
the amount of the mean daily variation in declination for the eleven 
years from 1834 to 1845 inclusive, which exhibit an increase from 
8-25 in 1834 to 1290 in 1836, whence a gradual and steady decline to 
7°41 in 1844. And from this (which as we now perceive falls in per- 
