21. The path which a ship describes, while she sails on the same point of the compass, and cuts all the meridians at the same angle, is called a rhumb line.

This angle is usually called the course, and sometimes the proper angle of the rhumb. If the rhumb line, which is a loxodromic or spiral curve, be continued, it will never return into itself so as to form a circle, except it happens to be due east and west, or due north and south; and it can never be a straight line upon any map, except the meridians be parallel to each other, as in Mercator's and the plane chart. Hence the difficulty of finding the true bearing between two places on the terrestrial globe, or on any map but those above mentioned. The bearing found by a quadrant of altitude on a globe, is only the measure of a spherical angle upon th surface of that globe, as defined by the angle of position, and not the real bearing or rhumb, as shown by the compass; if a place A bear due east from a place B, the place B will bear due west from the place A; but this is not the case when measured with a quadrant of altitude.

QUESTIONS.

How many positions of the sphere are there? What is a right sphere, and what inhabitants of

the earth have this position?

What is a parallel sphere, and what inhabitants of the globe have this position?

What is an oblique sphere, and what inhabitants of the globe have this position?

What inhabitants are called antæci to each other, and what do you observe with respect to their latitudes, longitudes, &c. ?

What inhabitants are called periæci to each other, and what is observed with respect to their latitudes, longitudes, hours, &c. ?

What are the antipodes, and what observed with respect to their seasons of the year, &c.?

What parts of the globe do the amphiscii inhabit, and why are they so called?

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When do the amphiscii obtain the name of ascii?

What parts of the globe do the heteroscii inha

bit, and why are they so called ?

What parts of the globe do the periscii inhabit,

and why are they so called?

What is the right ascension of the sun?

What is the oblique ascension of the sun?
What is the oblique descension of the sun?

What is the ascensional or descensional differ

ence?

What is the crepusculum, or twilight, and when does it begin or end?

What is an angle of position?
What are rhumbs and rhumb lines?

CHAPTER. IX.

Astronomical and Geographical Problems performed by the Terrestrial Globe.

PROBLEM I.

A Place being given, to find its Latitude and Longitude.

RULE. Bring the given place to the graduated side of the brazen meridian, which is counted from the equator towards the poles; the degree directly over the place is the latitude, and the degree on the equator, under the edge of the meridian, is the longitude.

The longitude is either east or west. Thus, if it be on the east side of the first meridian, it is called east longitude; if on the west side, west longitude, and is reckoned 180 degrees each way.

On Wilson's American globes there are two rows of figures on the north side of the equator. When the place lies on the east side of the meridian of London, the longitude must be counted on the upper line; and when it is on the west side, it must be counted on the lower line.

It has been already observed that the places on the earth are laid down on the terrestrial globe, so as to answer to their real situations: Hence the latitude and longitude of a place on the terrestrial globe, found according to the above rule, will be the true latitude and longitude of the same place, situated on the real globe of the earth.

EXAMPLES.

1. What is the latitude and longitude of NewYork, the first commercial city in America, and one of the first in the world ?

Bring New-York to the graduated side of the meridian, and it will be found under about 40° 42' north of the equator, or 40° 42' north latitude; and the intersection of the meridian with the equator is 740 west of the meridian of London, or 740 west longitude. Hence New-York is in 40° 42' north latitude, and 740 west longitude.

It is proper to observe that the latitudes of places cannot be found on the terrestrial globe to any great degree of accuracy, because the brazen meridian is only graduated to degrees and half degrees, and seldom to less than quarter degrees; the same defect is in the graduation of the horizon and quadrant of altitude; but the equator is usually graduated to degrees and minutes. Consequently, whenever the latitude or longitude of a place is to be found accurately, we must have recourse to correct tables, calculated for that purpose: for instance, the latitude of New-York, found by calculation, is 40° 42′ 40′′ north, and the longitude 74° 1' west.

2. Required the latitude and longitude of Washington city, the capital of the United States.

3. Find the latitude and longitude of London, the capital of England.

4. Required the latitude and longitude of Copenhagen, the capital of Denmark.

5. What is the latitude and longitude of Paris, the capital of France?

6. Required the latitude and longitude of Dub

lin, the capital of Ireland.

VA

7. What is the latitude and longitude of Philadelphia, the capital of Pennsylvania?

It may not be improper to remark, that capital, in this work, generally implies the chief or largest city in a State; and the seat of government, the town or city where the legislature of the State meets: for instance, Harrisburg is the seat of government of the State of Pennsylvania, and Philadelphia the capital or chief city.

8. What is the latitude and longitude of Madrid, the capital of Spain?

9. What is the latitude and longitude of Moscow in Russia?

10. What is the latitude and longitude of Canton in China?

11. What is the latitude and longitude of St. Helena, an island in the Atlantic Ocean, in which Napoleon Bonaparte was imprisoned by the allied sovereigns of Europe, from the year 1815 till his death in 1821?

PROBLEM II.

To find all those places that have the same latitude as any given place.

RULE. Bring the given place to the brazen meridian, and mark the degree over it; turn the globe round, and all places passing under the observed degree of latitude, are those required.

Whenever a place is brought to the brazen meridian, the graduated edge which is numbered from the equator towards the poles, is always to be understood, unless the contrary be mentioned.

All places in the same latitude, as has been already observed, have the same length of day and night, and the same seasons of the year, though, from local circumstances, they may not have the same atmospherical temperature.

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EXAMPLES.

1. What places have the same latitude, or nearly the same latitude as Baltimore, the capital of Maryland, in latitude 39° 20' north?

Answer. Flores, one of the Western Islands; Cagliari, the capital of Sardinia; Port Mahon in Minorca; Sarmacand, once the capital of Independent Tartary; Pekin, the capital of China; Marietta, the oldest town in the state of Ohio, &c.

2. Which places have the same latitude, or nearly the same latitude with Madrid ?

3. What inhabitants of the earth have the same length of days as those of Berlin, the capital of Prussia?

4. What inhabitants of the earth have the same seasons of the year as those of Ispahan, formerly the capital of Persia ?

5. Find all the places on the globe which have no latitude, or which have nearly the same latitude with Quito, the largest city in the Republic of Colombia, famous for its great elevation, being upwards of 9500 feet above the level of the sea.

6. Find all the places on the globe which have the greatest latitude, or 90 degrees.

7. Which places have nearly the same latitude with Havana, the capital of Cuba?

8. Which places have nearly the same latitude with Rio Janeiro, the capital of Brazil?

9. Which places of the earth have nearly the same latitude with North Cape in Lapland, latitude 71° 10' north?

10. What places have nearly the same latitude as the following places: New-York; Petersburgh, the capital of the Russian empire; Canton in ChiIn Sydney, the capital of the British colony of