Now if our observer describe a circle, and draw a diameter inclined
according to above table, this diameter would represent the sun's
equator if the axis of the sun were square to the ecliptic-plane. But
this axis is slightly inclined, the effect of which is, that on or about
June 10 the sun is situated as shown in fig. 14 with respect to the
ecliptic _ab_; on or about September 11 he is situated as shown in fig.
13; on or about December 11 as shown in fig. 12; and on or about March
10 as shown in fig. 15. The inclination of his equator to the ecliptic
being so small, the student can find little difficulty in determining
with sufficient approximation the relation of the sun's polar axis to
the ecliptic on intermediate days, since the equator is never more
_inclined_ than in figs. 12 and 14, never more _opened out_ than in
figs. 13 and 15. Having then drawn a line to represent the sun's
ecliptical diameter inclined to the horizontal diameter as above
described, and having (with this line to correspond to _ab_ in figs.
12-15) drawn in the sun's equator suitably inclined and opened out, he
has the sun's actual presentation (at noon) as seen with an erecting
eye-piece. Holding his picture upside down, he has the sun's
presentation as seen with an astronomical eye-piece--and, finally,
looking at his picture from behind (without inverting it), he has the
presentation seen when the sun is projected on the screen. Hence, if he
make a copy of this last view of his diagram upon the centre of his
screen, and using a low power, bring the whole of the sun's image to
coincide with the circle thus drawn (to a suitable scale) on the screen,
he will at once see what is the true position of the different
sun-spots. After a little practice the construction of a suitably sized
and marked circle on the screen will not occupy more than a minute or
two.

[Illustration: _Fig. 12._]

[Illustration: _Fig. 13._]

[Illustration: _Fig. 14._]

[Illustration: _Fig. 15._]

It must be noticed that the sun's apparent diameter is not always the
same. He is nearer to us in winter than in summer, and, of course, his
apparent diameter is greater at the former than at the latter season.
The variation of the apparent diameter corresponds (inversely) to the
variation of distance. As the sun's greatest distance from the earth is
93,000,000 miles (pretty nearly) and his least 90,000,000, his greatest,
mean, and least apparent diameters are as 93, 91-1/2, a