MarcH 10, 1904] 
NATURE 
447 
SUN-SPOT VARIATION IN LATITUDE, 
1861-1902. 
4 VERYONE who is acquainted with sun-spot statistics 
is familiar with the law known as ‘‘ Sporer’s law of 
Sun-spot zones,’’ which was derived after a laborious series 
of sun-spot observations made by Sporer himself. Previous 
to this indefatigable worker, Carrington made a series of 
most valuable observations between the years 1853 and 
1861, and it was he who first directed attention to the fact 
that sun-spots had a general drift towards the equator 
during a sun-spot cycle. To use his own words, he stated 
that there was indicated ‘‘ a great contraction of the limiting 
parallels between which spots were formed for two years 
previously to the minimum of 1856, and, soon after this 
epoch, the apparent commencement of two fresh belts of 
spots in high latitudes, north and south, which have in 
Subsequent years shown a tendency to coalesce, and ulti- 
mately to contract, as before, to extinction.” 
Discussing these and his own observations, Spérer was 
led not only to corroborate the deductions made by Carring- 
ton, but to formulate more definitely a law of sun-spot 
circulation, which he stated as follows :— 
“Un peu avant le minimum, il’n’y a de 
taches que prés de l’equateur solaire, entre 
+5° et —5°. A partir du minimum, les 
taches, qui avaient depyis longtemps 
déserté les hautes latitudes, s’y montrent 
brusquement vers +30°. Puis elles se 
multiplient, un peu partout, a peu prés 
entre ces limites, jusqu’au maximum, mais 
leur latitude moyenne diminue constam- 
ment jusqu’a 1’époque du nouveau mini- 
mum.”’ 
To arrive at this result Sporer made a 
prominences appear on any part of the disc, it was 
Sufficient, in order to trace their distribution through- 
out a year, to divide the sun’s surface into nine zones of 
10 degrees each. Since, however, spots seldom occur above 
latitude 40°, the width of the zones had to be considerably 
diminished. For the present inquiry, it was decided to 
group the spots into belts 3 degrees wide, for even zones 
of 5 degrees in width were found to mask many important 
characteristics. 
The necessity for such narrow zones will be seen from 
the accompanying figure (Fig. 1), in which the yearly dis- 
tribution of spots is shown for the years 1879-1883, taking 
zones of 10 degrees, 5 degrees, and 3 degrees in width 
respectively. 
In these curves each broad vertical line corresponds to 
the solar equator, and the scales to the right and left of 
each represent the north and south latitudes respectively. 
The heights of the curves above each horizontal zero line 
indicate the different amounts of spotted area, and the 
scales of these are so arranged that the curves are all pro- 
portional to the spotted area. 
The curves themselves are formed by determining the 
very complete investigation of the position 
of every sun-spot that had been observed 
up to that time in relation to the solar 
equator. In fact, he brought together all 
the statistics of the latitudes of sun-spots 
1382 
for each hemisphere, and determined . for 
each period of the sun’s rotation the mean 
heliographic latitude of the spotted area. 
To indicate the variation from year to year 
of this mean heliographic latitude he pub- 
dished curves, and the special feature of 
these was that each commenced in high 
Jatitudes about the time of sun-spot mini- 
mum, and gradually approached the 
equator until the epoch of the following 
minimum, when a new cycle commenced 
in high latitudes, the two curves over- 
lapping for a short time about the time 
of sun-spot minimum. 
If Sporer’s curves be closely examined 
it will be found that those which pass 
strictly through the actual points given by 
observation are of a wavy nature, and are 
sometimes above and below the mean 
curve from which Sporer deduced his law. In 
fact, Sporer himself directed attention to this peculiarity, 
and distinctly remarked on the subsidiary increases of 
spotted area and a reversion of spots to higher latitudes 
at times other than at sun-spot minimum. In later times 
Dr. Braun, of the Kalésca Observatory, pointed out similar 
anomalies from his own observations made between 1880 
and 1884. ; ; : 
From the illustration (Fig. 2) accompanying this article 
curves B indicate the wavy nature of these mean_helio- 
‘graphic curves, and it will be noticed that even up to the 
present time this peculiarity is a marked feature. 
It was with the object of attempting to trace the origin 
of these variations—variations which indicated that 
Sporer’s law might be only of a very general nature—that 
a recent investigation was commenced, the results of which 
were communicated to the Royal Society (February 11). 
The method of analysis was to divide the limited region 
on the sun’s surface in which spots appear into strips or 
zones, in a similar way to that employed in the study of 
the prominences (Nature, vol. Ixvii. p. 570). As_ solar 
NO. 1793, VOL. 69] 
eee 
40 30 20-10 0 40 20 30 40 40 30 20-10 0 
Ss N s 
TEN DECREE ZONES. 
————— = 
30 40 
= 
¥ (eae ta > sont —— ~ 
+10 20 40 30 20-10 O +10 20 30 40 
N S N. 
FIVE-DEGREE ZONES THREE -OEGREE ZONES. 
Fic. 1.—Distribution of Sun’s Spotted Area. 
mean spotted area for each zone, and plotting each value 
at the point representing the mean latitude of this zone; 
these points are then all joined together. Thus, in the 
case of the o-10° zone, the mean spotted area is plotted at 
5°, 10-20° at 15°, &c. The other zone divisions are 
similarly treated; thus o-5° is plotted at 2-5°, o-3° at 
° Q, 
Le Sues 
In the 10° zone curves here shown there is only one 
maximum in each hemisphere for the years in question, and 
these, as indicated by the dotted curves which join them, 
do not progress gradually towards the equator as would 
probably be the case according to Spérer’s law. With 5° 
zones it is possible to detect the presence of two maxima 
in one or other of the hemispheres, all of which have a 
trend towards the equator in succeeding years. Still more 
detail is displayed in the 3° zones, and here is apparent a 
spot distribution and movement which is practically masked 
in the two preceding sets of curves. 
The advisability of adopting 3° zones being thus apparent, 
the whole series of observations from the year 1861-1902 
was treated in the above manner, the points plotted, and 
