would have passed 90 deg.. When it set in the west it would
have traversed half the circle, or 180 deg.. In Fig. 20 the angle of the
lines measured on the graduated arc is 10 deg.. The mountain is 10 deg.
high, the world 10 deg. in diameter, the comet moves 10 deg. a day, the
stars are 10 deg. apart. The height of the mountain, the diameter of the
world, the velocity of the comet, and the distance between the
stars, depend on the distance of each from the point of sight. Every
degree is divided into 60 minutes (marked '), and every minute into
60 seconds (marked ").

[Illustration: Fig. 20.--Illustration of Angles.]

Imagine yourself inside a perfect sphere one hundred feet in diameter,
with the interior surface above, around, and below studded with
fixed bright points like stars. The familiar constellations of
night might be blazoned there in due proportion.

If this star-sprent sphere were made to revolve once in twenty-four
hours, all the stars would successively [Page 60] pass in review.
How easily we could measure distances between stars, from a certain
fixed meridian, or the equator! How easily we could tell when any
particular star would culminate! It is as easy to take all these
measurements when our earthly observatory is steadily revolved
within the sphere of circumambient stars. Stars can be mapped as
readily as the streets of a great city. Looking down on it in the
night, one could trace the lines of lighted streets, and judge
something of its extent and regularity. But the few lamps of evening
would suggest little of the greatness of the public buildings, the
magnificent enterprise and commerce of its citizens, or the
intelligence of its scholars. Looking up to the lamps of the
celestial city, one can judge something of its extent and
regularity; but they suggest little of the magnificence of the many
mansions.

Stars are reckoned as so many degrees, minutes, and seconds from
each other, from the zenith, or from a given meridian, or from the
equator. Thus the stars called the Pointers, in the Great Bear,
are 5 deg. apart; the nearest one is 29 deg. from the Pole Star, which is
39 deg. 56' 29" above the horizon at Philadelphia. In going to England
you creep up toward the north end of the earth, till the Pole Star
is 54 deg. high. It stays near its place among the stars continually,

"Of whose true-fixed and resting quality
There is no fellow in the firmament."

_How to Measure._

Suppose a tele