PROBLEM III.

TERRESTRIAL GLOBE.

To find the Difference of Latitude of two places. Repeat the Definitions given for Problem II. Repeat also, Zones, def. 71.

RULE. If both places be in the same hemisphere, subtract the less latitude from the greater. If one be in the northern and the other in the southern hemisphere, the sum of their latitudes is the difference required.

"The cultivated vegetables which form the necessaries or luxuries of human life, are each confined within limits, narrow, when compared with the whole surface of the earth; yet, almost every part of the earth's surface is capable of being abundantly covered with one kind or other of these. When one class fails, another appears in its place. Thus corn, wine, and oil, have each its boundaries."

1. Find the difference of latitude between Dublin and Lassa? (N.B. Both places north.)

"Wheat extends through the old Continent from England to Thibet; but it stops soon in going northwards, and is not found to succeed in the west of Scotland. Nor does it thrive better in the Torrid Zone than in the polar regions. Within the Torrid Zone, wheat, barley, and oats, are not cultivated, excepting in situations considerably elevated."

2. Difference of Latitude between Teneriffe and Bourdeaux. Bourdeaux and the Cape of Good Hope. (N.B. One place north, and the other south.)

"In both hemispheres, the profitable culture of the vine ceases within 30° of the Equator; unless in elevated situations, or in islands, as Teneriffe."

3. Difference of latitude between Charleston (South Carolina,) and Turin-Between Genoa and S. Point of Java-Between Cape St. Mary (S. Point of Madagascar,) and Bencoolen.

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"In the north of Italy, west of Milan, we first meet with the cultivation of rice. Rice extends all over the southern part of Asia, wherever the land can be, at pleasure, covered with water. In great part of Africa millet is one of the principal kinds of grain."

4. Find the difference of latitude between Halifax (Virginia), and the mouth of the Volga.

Between Rio Janeiro and the north point of Niphon (Japan).

"Cotton is cultivated to latitude 40 in the new world, but extends to Astracan in latitude 46 in the old."

For the same products we must search several degrees nearer to the Equator in the American Continent than in the Old World. This is owing to the difference of temperature alone, the soil of America being naturally as rich as that of any portion of the earth.

5. Find the difference of latitude between Canton and Nankin.

The tea plant is seldom cultivated farther north than the 30th degree of latitude; and thrives best between that and the Torrid Zone.

6. Find the difference of latitude between Manilla (Luzon, of the Philippines,) and Owhyhee.

Between N. of Owhyhee and the southernmost of the Feejee Islands.

The bread-fruit tree first appears in the Manillas, and "thence extends its benefits through innumerable islands in the Indian and Pacific Oceans."

7. Find the difference of latitude between Delhi and Cayenne.

Between the south point of Florida and Port Royal, Jamaica.

"The sugar cane, the plantain, the mulberry, the betel nut, the indigo tree, the tea tree, repay the labours of the cultivators in India and China, and several of these plants have been transferred with success to America and the West Indies."

H

PROBLEM IV.

CELESTIAL AND TERRESTRIAL GLOBES.

To find the Declination of a given Star, and the places which pass directly underneath it, as the earth rotates.

Repeat the following:—

Celestial Globe, (def. 11); Fixed Stars, (def. 4); Constellations, (def. 6); Greek Alphabet, (page 24); Equinoctial, (def. 14); Declination, (def. 17); Read over "Rhymes on the Constellations," (Appendix).

RULE.-Bring the given star to the upper semicircle of the brass meridian of the celestial globe, and the degree coinciding with the star will show its north or south declination.

Place the thumb-nail (of the right or left hand accordingly, see Prob. II.) upon that part of the brass meridian of the terrestrial globe which agrees in number and position with the declination of the star; and cause this model of our earth to rotate toward you, as you stand eastward of its south pole. The places which pass under the thumbnail will be those daily passing under the given star, which, on this account, is said to culminate vertically.

1. Find the declination of "Castor," (a of Gemini); and note down some of the principal places which daily pass exactly underneath it.

Answer. 321° north declination. Places, Nankin, (nearly,) Lahore, Ispahan, &c., &c.

2. Find the declination of "Rigel," (8 in the heel of Orion); and name any particular islands, and other places,

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to the inhabitants of which it appears to pass vertically, or nearly vertically.

3. Find the declination of ♪ of Orion, and the places that daily have it in their zenith.

Also y of Virgo

ditto

urus")

ditto

Remark. Every heavenly body, at any instant of time, sheds its direct beams over an exact half of our earth's

surface; and, in the absence of overpowering rays, (as of the sun or moon,) may be seen, in clear weather, by all the inhabitants of that half-surface.

But the latitudes of the regions contained in that halfsurface, will depend upon the heavenly body's declination. Thus, whilst a star, which, like 8 of Orion, is in the Equinoctial (i. e., without declination, and therefore vertical to our Equator,) sheds its beams from pole to pole, and is viewed in all latitudes; the beams of a star situated northward of the Equinoctial, (as Arcturus 20° N.D., drawn in the preceding figure,) must fall short of the south pole to an extent equal to its north declination; and accordingly, be perpetually invisible to the inhabitants of a certain southern portion of our globe.

But, for the same reason, the beams of that star will shine over the north pole, (see “T (terminator) of Arcturus" in the figure,) and can never be absent from a corresponding region of the northern hemisphere.

The same remarks apply, vice versa, to stars having south declination; such as Fomathaut, (see figure.)

TERRESTRIAL GLOBE.

The declination of a star, &c., being given, (or the latitude in which it culminates vertically,) to find to what places it is constantly above the horizon, and where it cannot rise.

Repeat the following:

Terminator, (def. 30); "Rhymes on the Constellations," six verses, (Appendix); Read "Double Stars," (see Index); “Variable Stars," (see Index).

RULE.-Elevate the pole to the star's declination; or, which is the same thing, to the latitude in which it culminates vertically; and the wooden circle of the globe will then represent the terminator, or constant boundary of that star's beams.*

Cause the globe to rotate (eastward) on its axis, and it

*It will be useful to rest a small coin, as a fourpenny-piece, upon the brazen meridian, with its centre coinciding with the declination, to represent the star.