Any one may see the spots on the sun who has a spy-glass. Darken
the room and put the glass through an opening toward the sun, as
shown in Fig. 37. The eye-piece should be drawn out about half
an inch beyond [Page 96] its usual focusing for distant objects. The
farther it is drawn, the nearer must we hold the screen for a
perfect image.
By holding a paper near the eye-piece, the proper direction of
the instrument may be discovered without injury to the eyes. By
this means the sun can be studied from day to day, and its spots or
the transits of Mercury and Venus shown to any number of spectators.
[Illustration: Fig. 37.--Holding Telescope to see the Sun's Spots.]
First covering the eyes with very dark or smoked glasses, erect
a disk of pasteboard four inches in diameter between you and the
sun; close one eye; stand near it, and the whole sun is obscured.
Withdraw from it till the sun's rays just shoot over the edge of
the disk on every side. Measure the distance from the eye to the
disk. You will be able to determine the distance of the sun by
the rule of three: thus, as four inches is to 860,000 miles, so
is distance from eye to disk to distance from disk to the sun.
Take such measurements at sunrise, noon, and sunset, and see the
apparently differing sizes due to refraction.
[Page 97]
VI.