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DIFFERENCE OF LATITUDE, ETC.
"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."
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,
DECLINATION AND LATITUDE.
to the inhabitants of which it appears to pass vertically, or
3. Find the declination of ♪ of Orion, and the places that daily have it in their zenith.
Remark. sheds its direct beams over an exact half of our earth's
Every heavenly body, at any instant of time,
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 Fomalhaut, (see figure.)
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.
DECLINATION AND LATITUDE.
will be seen that all places not more distant from the elevated pole than the given star is from the equinoctial, cannot lose its rays; whilst those within a corresponding distance of the other pole, cannot receive them. Note down those places.
1. Find those places to which the following stars never rise, and those places also where they are perpetually above the horizon.
a of Eridanus, "Achernar," (between the body of the Whale and the South Pole), 58° S. D.
Here, elevating the South Pole 58°, the wooden circle of the globe represents the terminator or boundary of the latitudes which the star's rays can reach, and I find by turning the globe, that whilst this star is always above the horizon of the southern portions of Africa, America, and New Holland, and of the whole of New Zealand, &c., it is not seen from the extreme north of Africa and Arabia; and is, of course, always absent from all Europe and the greater part of North America and Asia.
a of the Southern Fish, "Fomalhaut," (near the tail of Cetus).
B of Perseus, "Algol" (in the head of Medusa) 40
8 of Cetus
2. How far over the North Pole can the rays of Capella, (8 of Auriga, N. D. 453,) diffuse themselves; and at what places can Capella never be seen to set?
3. How far short of the South Pole do Capella's rays reach; and from what places on our earth can Capella never be viewed?
4. If the Pole-star (a of Ursa Minor,) were exactly at the Polar point, from which part* of our earth would it never be seen?
5. The Pole-star is about 110 from the Polar point, or has a little less than 88° 27' of north declination: at what places, therefore, is it some time above the horizon, (although only at a little elevation,) besides those north of the Equator?
* i. e. disregarding the effects of refraction.