226 Original Articles. [April 
The earliest observers of the solar spots were led to notice the fact 
of their total absence in the circumpolar regions of the sun’s surface, 
and we find it already remarked by Scheiner that their appearance is 
confined to a zone extending to 30° or 35° in latitude on either side of 
his equator, All subsequent observation has confirmed this. Only 
one fully-authenticated observation (by M. Peters, in 1846) is ad- 
duced of a spot in so high a North latitude as 50°, and a double one 
has been observed by Mr. Carrington in 44° §. The equator itself is, 
however, rarely visited by them, and this paucity usually extends over 
an equatorial zone, from 8° N. to 8° 8. latitude. From these limits 
to 20° latitude on either side extends the region of their most frequent 
occurrence. Moreover it is no uncommon thing in very spotty states 
of the sun to observe some one parallel of latitude dotted out as it 
were on the disc by a more or less continuous line of spots extending 
across or nearly across the whole disc, and that occasionally in both 
hemispheres. (See Fig. 7.) 
No one meridian of the sun, however, is found to be especially 
abundant in them, nor has observation yet pointed out any particular 
locality on that globe, at or near which a spot more frequently breaks 
out than at any other on the same parallel, a circumstance conclusive 
against their owing their origin to volcanic eruptions or any simply 
local causes. 
The sun is not equally spotted at all times. Many months and 
sometimes whole years have elapsed without the notice of a spot. In 
others, for months, nay years together, they have been remarkable for 
number and magnitude. It seems to have been a very general belief up 
to the epoch of Professor Schwabe’s observations already mentioned, that 
this variety was purely casual, and altogether irregular. But the evidence 
obtained by M. Schwabe, observing from 1826 to 1860, on an average 
300 days per annum, during each of which the number of groups and 
single spots was registered, clearly established a periodicity. Thus, in 
1833, 1848, 1856, very few groups were seen, and on nearly half the 
days of observation the sun was spotless ; while in 1828, 1837, 1848, 
1859, and 1860, the number of groups was extraordinary, and not one 
spotless day occurred; while the intermediate years exhibited a 
regular alternate increase and decrease. A period from ten to twelve 
years in duration was thus indicated. It became therefore exceedingly 
interesting to ascertain, by the collection and comparison of all the ob- 
servations recorded of the sun’s state since the first discovery of the 
spots, whether this alteration of periods of excitement and quiescence 
would be corroborated or not. This task (one of no slight labour) has 
been accomplished with extraordinary devotion and perseverance by 
Dr. Rudolf Wolf, Professor of Astronomy at Zurich, who in a series of 
Essays communicated to and published by the Zurich Society of Na- 
tural Philosophy, has collected from every available source the whole 
literature of the subject, and subjected the totality of the recorded ob- 
servations to a most careful and searching scrutiny. In so doing he 
has been enabled to assign, on what appears to us sufficient evidence in 
general, and in most cases decisive, the following epochs of minima 
