324 Researches on Solar Physics. 
parts of his apparent disk. We have not hitherto attempted the 
former inquiry (although the subject is not lost sight of, but may 
come within the range of our future researches), but have con- 
fined ourselves entirely to the latter, and now proceed to des- 
cribe the method of observation adopted. 
41. Suppose the visible disk of the sun to be cut up into sec: 
tions by great circles passing through these poles. These great 
circles may be regarded as lines of longitude, only, in the present 
instance, they are not supposed to move round with the sun’s 
surface, but rather to be connected with the earth in such a man- 
ner that the plane which passes through the earth is always 
reckoned the zero or meridian. 
Now it is well known that the pole of the sun differs very 
little from that of the ecliptic, and therefore, in an approximate 
investigation like the present, we may suppose the two to coin- 
cide; these longitudes will thus denote ecliptical longitudes, and 
the longitude in which the earth is placed being called zero, we 
may with propriety reckon those to the left negative, and those 
to the right positive. A sun-spot as it movés across the disk on 
account of rotation will thus appear at a longitude —90°, and 
vanish at a longitude +90°. 
The same course will be pursued by the inferior planets Mer- 
cury and Venus, which move faster than the Earth; while, on 
the other hand, the superior planets, which move slower than the 
Earth, may be supposed to pursue an opposite course, passing 
across the circles of longitude from right to left. 
42. It will thus be apparent that, if the behavior of sun-spots 
is at all influenced by the positions of the planets, the fact 18 
likely to be discovered by this means. Thus if all the prominent 
a be in the same longitude as the Earth, if there be a bond 
between sun-spots and planets, we should be entitled to expect 
im such a case some change in appearance or size when the spots 
for that period pass the central line; if, on the other hand, these 
planets be together at 20° to the right of the Earth, we might 
expect some change at 20° to the right, and so on. In fine, one 
of our objects in the present research is to ascertain the compar 
ative size, at the different ecliptical longitudes in the visible disk, 
of the whole spotted area for any period, the mass of observations 
being broken up for this purpose into periods embracing perhaps 
three or four months, so as to comprehend in each a sufficient 
number of groups. 
_ 48. For this purpose the following plan was adopted. A sub- 
sidiary table was formed in which the whole visible disk was 
portioned out into thirteen parts, each part denoting a days 
progress of a spot and embracing every 14° of longitude from 
—90° to +90°. Hach of these parts had in this table two col- 
umns allotted to it, in one of which the exact longitude of 
