always the fame, though his longitude would be continually changing.

But if he went directly north or fouth, his longitude would continue the fame, but his latitude would be perpetually varying.

If he went obliquely, he would change both his latitude and longitude.

The longitude and latitude of places give only their relative distances on the globe; to discover, therefore, their real distance, we have recourfe to the following problem.

PROBLEM X.

Any place being given, to find the distance of that place from another, in a great circle of the earth.

We shall divide this problem into three cafes.

Cafe 1. If the places lie under the fame meridian. Bring them up to the meridian, and mark the number of degrees intercepted between them. Multiply the number of degrees thus found by 60, and they will give the number of

geogra

geographical miles between the two places. But if we would have the number of English miles, the degree before found must be multiplied by 692.

Cafe 2. If the places lie under the equator. Find their difference of longitude in degrees, and multiply as in the preceding case, by 60, or 69.

Cafe 3. If the places lie neither under the fame meridian, nor under the equator. Then lay the quadrant of altitude over the two places, and mark the number of degrees intercepted between them. These degrees multiplied as abovementioned, will give the required distance.

A PARALLEL SPHERE is that pofition of the globe, in which the poles are in their zenith and nadir, it's axis at right angles to the equator and horizon, which coincide; confequently, thofe circles which are parallel to the equator, are alfo parallel to the horizon.

The inhabitants that answer to this pofition of the fphere, if any there be, muft live upon the two terreftrial poles, and will have but one day and one night throughout the year, each fix

months

months long. The day, to those who live under the north pole, begins when the fun enters Aries, and continues till he reaches Libra, when night commences, and continues the other fix months. Those who live under the fouth pole, experience the direct contrary; but both enjoy a long continuance of twilight, after the fun has departed from them, and before he appears again.

For half a year, the inhabitants of the pole fee the fun moving continually round above their horizon, in a kind of spiral line; when they first perceive him, he fkims, as it were, their horizon, then rifes gradually higher, till he reaches the tropic, when he again defcends, till he touches the horizon, when their long and gloomy night begins.

During their fummer's day, the moon appears to them in the heavens only as a white cloud; in the winter, during her fecond and third quarters, fhe circulates above the horizon for feveral days, without fetting, being a fortnight above, and a fortnight below the horizon.

They can only fee the ftars in that hemifphere between the pole and the equator; during half a year, none of them are vifible, being swallowed

up,

1

up, as it were, by the fuperior light of the fun. To them the ftars never fet, but move in circles parallel to the horizon, keeping always the fame altitude. The planets are half their time above, and half below the horizon.

A RIGHT SPHERE is that in which the equator is at right angles to the horizon, and therefore in the zenith and nadir, and in which the poles are in the horizon.

The inhabitants that answer to this fituation of the sphere, live under the equator; their days and nights are of an equal length throughout the year, being each of them twelve hours in length.

The fun rises and sets nearly perpendicular; he is half a year on one fide their zenith, and as much on the other, paffing over it twice a year at the equinoxes.

There is nothing uncommon in the appearance of the moon, but her rifing and fetting like the fun, nearly in a perpendicular direction; but there is to these inhabitants a moft glorious difplay of all the stars in the heavens, from pole to pole, all of them rifing and fetting perpendicular,. except the poles which lie in the horizon.

An

An OBLIQUE SPHERE is the pofition common to all the inhabitants of the earth, except those who live at the poles, and upon the equator; it is thus named, because the equator cuts the horizon obliquely.

In this sphere the axis of the earth always makes an acute angle with the horizon; the equator is half above and half below it.

All the parallels to the equator cut the horizon alfo obliquely, and thus make the diurnal arches greater or less than the nocturnal ones, excepting at the time of the equinoxes.

Those inhabitants of this fphere, who live without the tropics, never have the fun in their zenith; but under the tropics the fun is vertical once, and between the tropics and the equator twice every year.

In this pofition the stars rife and set obliquely; and as the moon, when at full, is always in an oppofite fign to the fun, fhe is on the fouth fide of the equator in fummer, and consequently her altitude is low, and her courfe fhort; but in winter, when at the full, fhe is in the northern