An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

16 THE EARTH.
through the poles of the ecliptic, at the distance of 23~ degrees
from the pole of the earth. (Art. 33.)
41. The earth is divided into five zones. That portion of
the earth which lies between the tropics, is called the Torrid
Zone; that between the tropics and the polar circles, the
Temperate Zones; and that between the polar circles and the
poles, the Fri4gid Zones.
42. The Zodiac is the part of the celestial sphere which lies
about 8 degrees on each side of the ecliptic. This portion of
the heavens is thus marked off by itself, because the planets
are never seen further from the ecliptic than this limit.
43. The elevation, of the pole is equal to the latitude of the
place.
The arc PE (Fig. 4.)=ZO.. PO=ZE,which equals the latitude.
44. The elevation of the equator is equal to the complement
of the latitude.
ZH=90~. But ZE=Lat..~. EII- 90- Lat. = colatitude.
45. The distance of any place from the pole (or the polar
distance) equals the complement of the latitude.
EP= - 900. But EZ=Lat... ZP= 90 -Lat. = colatitude.
CHAPTER II.
DIURNAL REVOLIJTION-ARTIFICIAL GLOBES-ASTRONOMICAL
PROBLEMS.
46. THE apparent diurnal revolution of the heavenly bodies
from east to west, is owing to the actual revolution of the
earth on its own axis from west to east. If we conceive of a
radius of the earth's equator extended until it meets the concave sphere of the heavens, then, as the earth revolves, the ex