ON SOLAE PHYSICS. 
397 
“ The curves, as delineated for the three complete periods embraced, are highly inter- 
esting and instructive. They place in a very clear and unmistakable light the antici- 
pation in point of time of the occurrence of the maximum of maculiferous excitement 
before the middle of the total period which the present rapidly increasing number of 
spots actually in progress seems to promise fully to confirm for the period (lSGG’G- 
1877+) ; and here I cannot help observing that although the lengths of the three periods 
here embraced vary between 9’81 and 12'68 years, yet the mean of the three is almost 
exactly 11T, and this agrees with the whole course of the solar history since 1800, 
which was a year of maximum. Another point of much interest is the evaluation of 
the spotted area in numerical aliquots of the solar surface, showing to how very small 
an extent the sun is entitled to the character of a variable star (in so far at least as dimi- 
nution and increase of illuminated area are to be regarded as causes of variability). The 
total fluctuation arising from this cause it appears does not exceed about 2000 parts 
in a million, or about 5 -^ part of the total light, which in estimating the brightness 
of a star would be quite inappreciable*. The tendency to a double maximum, an 
earlier and a later, pointed out as analogous to those observed in /3 Lyra; and R. Sagittte, 
it may be worth noticing, has a similar though less strongly marked analogous feature 
in the light curve of r t Argus, as laid down for a periodic variation sixty-seven years in 
duration by Professor Loomis, which presents a subordinate maximum (followed by a 
rather marked depression) at about the twenty-sixth year, the principal one being 
deferred to the forty-fourth of the total period ; and this law is observed in three suc- 
cessive periods.” 
It has also been suggested to us by Sir AV. Thomson, in connexion with that part of 
our paper which refers to the possible connexion between sun-spots and planetary posi- 
tion, to take arbitrary periods, viz. three-fourths of the planetary period, which we have 
taken, and to compare the results of these with the results derived in our paper. We 
have done this in the case of Venus and Jupiter, and also in that of Venus and Mercury, 
and have obtained the following numbers : — 
Three-fourths of the period 
Three-fourths of the period 
of Venus and Jupiter. 
of Venus and Mercury. 
-117 
- 184 
-287 
- 754 
— G94 
-1G21 
-631 
-1196 
-461 
+ 567 
-140 
+ 1764 
+ 441 
+ 848 
+ 310 
- 466 
-139 
— 605 
We have not lost sight of the very small amount of variation 
in the brightness of the solar 
MDCCCLXX. 
3 1 
