284 
NATURE 
[ Fan. 13, 1870 
ON THE PERIODICITY OF THE SOLAR SPOTS 
eee of our readers are aware that the Kew ob- 
sétvets, Messrs. De la Rue, Stewart, and Loewy, 
have for some time past beeh efigaged in investigations, 
which, as far as they have already extended, go to show that 
there is an intimate and, as yet, unexplained connection 
between the configuration of the planets and the position 
and number of the spots on the sun, This result, 
which at orice séems to Jand us in a sort of modern astro- 
logy, and which is so extraordinary, is, we suppose, on 
that ground, for we know of no other, questioned by 
many European astronomers. In this state of the case, 
no apology is needed, then, for reproducing, from the 
Pyveéedings of the American Philosophical Society, the 
results of a Yecefit independent investigation of this 
subject by Dr. Kirkwood, together with some historical 
matter of some interest. 
Dr. Kirkwood commences by reminding us that the 
most ancient observations of sun-spots of which we have 
finy record, are those of the Chinese in the year 321 A.D. ; 
the first notice of their detection by Europeans being 
found in the annals of the Frankish kings. A black spot, 
according to Adelmus, was seen on the sun’s disc, 
March 17th, 807, and continued visible 8 days. Similar 
phenomena were again observed from the 28th of May 
to the 26th of August, A.D, 840. The year 1096 was also 
signalised by the appearance of spots so large as to be 
visible to the naked eye. The next date, in chronological 
order, is that of 1161, when a spot was seen by Averroés. 
Finally, on the 7th, 8th, and 16th of December, 1590, “a 
great blacke spot on the sunne,” apparently “about the 
bignesse of a shilling,” was observed at sea by those on 
board the ship “ Richard of Arundell.” The foregoing 
are, we believe, the only undoubted instances in which 
these phenomena were observed previous to the invention 
of the telescope. 
From 1610 to 1750 the sun was frequently observed 
through instruments of various optical power, and the 
sparseness, or even the entire absence of spots, during 
considerable intervals of time, as well as their great 
number and magnitude at other epochs, were noticed by 
different astronomers, We come now to a most inte- 
resting and most remarkable epoch in the history of solar 
physics—an epoch in which the periodicity of the spots 
gradually come out. 
The 11-Year Period of Schwabe-—In 1826, Hofrath 
Schwabe, of Dessau, commenced a series of sun-spot 
observations, which have been continued without inter- 
ruption to the present time (1869), 
Schwabe has shown a very marked periodicity in the 
spots ; the interval between two consecutive maxima or 
minima being, according to him, about 10 years. Soon after 
the announcement of this interesting discovery, Dr. Lamont, 
of Munich, detected a corresponding decennial period in 
the variation of the magnetic needle; the epochs of 
maxima and minima in the latter coinciding with those in 
the former. These results have also been confirmed by 
other observers in places quite remote from each other ; 
so that the decennial magnetic cycle may be regarded as 
well established. The equality of this period with that of 
the solar spots naturally suggested the hypothesis of their 
intimate relationship. Such a causal connection may be 
difficult of explanation ; the fact, however, is placed beyond 
doubt by the researches of Wolf and Sabine.* The 
former, besides carefully observing the sun-spots since 
1847, has discussed all accessible recorded observations, 
both solar and magnetic, bearing on the subject. He had 
thus ascertained a number of epochs of maxima and 
* These magnetic variations, which will not be discussed in the present 
paper, are mentioned to give completeness of view to the phenomena under 
consideration. It is also worthy of remark that the Aurora Borealis is be- 
lieved to exhibit a corresponding periodicity. (We believe that Sir E. Sabine 
Was the first to remark the connection between sun-spots and magnetic dis- 
turbances.—Eb.] 
miniitia anterior to those observed by Schwabe,—from all 
of which he has determined the period of the spots to be 
Ir‘1r years. He undertakes to show, moreover, that this 
period coincides more exactly with that of the magnetic 
variation than the to-year cycle of Lamont. 
The 56-Vear Pertod—Besides Schwabe’s period of 
tr years, Wolf finds a larger cycle of 55 years, in which 
the solar activity passes through a series of changes. It 
is not, however, so distinctly marked as the cycle of 
Schwabe. Its last maximum was about 1837, and that 
preceding, about 1780, 
The 233-Day Period.—Professor Wolf, after carefully 
discussing his own and Schwabe’s observations, claims to 
have discovered two or three minor periods of solar 
activity. ‘By projecting all the results in a continuous 
curve, he finds in it a series of small undulations succeed- 
ing each other at an average interval of 7°65 months,” 
or 233 days. 
The 27-Day Period.—The same astronomer thinks 
he has detected a short period of variation corresponding 
to the sun’s time of rotation with respect to the earth, or 
about 27 days. 
The 584—-Day Pertod—De la Rue, Stewart, and 
Loewy, have found a period varying between 18 and 20 
months ; the mean being about 584 days. Other periods 
of maxima and minima will probably be detected; but those 
we have enumerated are perhaps the only ones sufficiently 
well established to justify any attempt at explanation. 
That the solar spots are produced in some way by the 
planetary disturbance of the photosphere, is now generally 
admitted. As yet, however, the manner in which this in- 
fluence is exerted can be little more than matter of con- 
jecture. If the action is analogous to that of the moon 
on the earth, the relative disturbing power of the different 
members of the system will be as follows : * 
Name. Mass. | In Aph. |At M. Dist.) In Perih. 
y | ( xavbrs1 (Encke) | 63 TIL 219 
| Mercury | V santos (Leverrier) | 102 180 355 
Venus | 40VeT1 203 207 211 
Earth | aia 95 100 105 
Mars 2004735 | z 3 4 
Jupiter rier | 194 214 | 236 
Saturn avon 8 10 12 
Uranus nylon ° ° ° 
Neptune | teisa | ° ° ° 
The connection between the number of sun-spots 
and the positions of the planets was noticed by Wolf as 
long since as 1858. In the interesting memoir of De la 
Rue, Stewart, and Loewy, the causal connection between 
the positions of Venus and Jupiter and the behaviour of 
sun-spots seems to be clearly established. An inspection 
of the Table shows that writers generally have given 
undue weight to Saturn’s influence. Again, although 
Mercury’s action at aphelion is but feeble, and even, at his 
mean distance, less than that of Venus or Jupiter, his 
perturbing power at ferthelion is the greatest of all 
planets—a fact which certainly demands consideration in 
any theory which refers the origin of solar spots to plane- 
tary agency. After giving the subject much study and 
attention, Dr. Kirkwood deems it impossible, w7thouwt the 
introduction of any modifying cause, to establisha general 
correspondence between the different sun-spot periods and 
those of regularly recurring planetary configurations. 
But the hypothesis that a particular portion of the 
sun’s surface is more favourable to spot formation—or, 
in other words, more susceptible to planetary influence 
—than others, will, he believes, obviate all difficulty, Is 
mt . 
* The table is derived from the formula 6 = aH where 8 represents the dis- 
turbing power of a planet, its mass, and @ its distance. 
