1864. | Henrscuen on the Solar Spot 229 
fectly with tho increase and decrease of the spots in that mterval, but 
without reference to them) he drew the conclusion above mentioned. A 
similar result was announced in 1852 by General Sabine, and extended to 
all the magnetic elements—connecting the periodicity with that of the 
spots, but assuming a period of ten years in accordance with M. 
Schwabe’s first conclusion—and to this period of magnetic change 
General Sabine we believe is still disposed to adhere. Professor 
Wolf, however, who has instituted the same system of inquiry into all 
available observations of magnetic declination, finds this element at 
least (so far as dependable observations exist) to vary in so perfect 
accordance with his law of solar activity that a table of its mean annual 
amounts as estimated in the manner above stated is convertible by a 
mere change of scale and the use of a multiplier constant for each 
magnetic observatory, into a table of mean decimal variations for the 
same years ineach. It will be recollected, however, that the earlier 
data here are sparingly scattered, and it would be premature to assert 
the absolute generality of this conclusion in the face of that to which 
the Astronomer Royal has been led by his recent elaborate discus- 
sion of the Greenwich magnetic observations from 1841 to 1857, viz. : 
that from the rapid decrease of dimension in the projected curves for 
the several years from 1848 to 1857, their forms remaining the same 
he is led to believe that in this interval “some great cosmical change 
has come upon the earth affecting terrestrial magnetism.” We should 
not pass quite unnoticed, however, that, granting the correctness of 
the epoch of maximum (1836) of Dr. Wolfs longer period of 56 years, 
this precise interval of time would fall upon the most rapid downward 
sweep of his average curve of maxima during its progress from the 
maximum of 1836 to that of 1892. 
A connection between the periodicity of the spots and the recurrence of 
great displays of aurora borealis has also been surmised, and was, indeed, 
suggested as a possibility by Mairan more than a century ago. The 
recent researches of Professor Fritz, grounded on a diligent assemblage 
and collection of recorded auroras instituted by Dr. Wolf, the late 
Professor Olmsted, and others, have placed this connection in a very 
distinct light, and shown not only that the 11-year period of the spots 
has its parallel in the annual frequency of auroras, both in respect of 
number and the epochs of minimum, but also that the long period of 
56 years is represented in that phenomenon, and, in fact, agrees better 
in indicating epochs of extraordinary abundance and paucity than a 
longer period of 65 years proposed by Olmsted, without reference to 
the spots. To dilate on the steps of this inquiry would lead us beyond 
our limits, and we hasten to the consideration of another class of 
phenomena, to which observations of Mr. Carrington, from 1853 to 
1861, recently published with the liberal aid of a grant from the Royal 
Society, have given a very prominent degree of interest, as affording at 
length a glimpse—if not of the physical cause in which the spots 
originate, at least of the working of a mechanism through which that 
cause may possibly produce its effect. 
We have already noticed, that while the results obtained by 
different observers and computists as to the position of the sun’s axis of 
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