riod perpendicular to the inhabitants that live at the equator.

By continuing to turn the handle, the earth advances in the ecliptic, and the terminator fhews how the days are continually decreasing, and the diurnal arches fhortening, till by degrees the whole space contained by the northern polar circle is on that fide of the terminator which is oppofite to the fun, which happens when the carth is got to the first point of Cancer, and the annual index is at the first point of Capricorn, on the 21st of December. In this ftate of the globe, the northern polar circle, and all the country within that space, have no day at all; whilst the inhabitants that live within the fouthern polar circle, being on that fide of the terminator which is next the fun, enjoy perpetual day. By this and the former fituation of the earth, you will obferve, that there are nations to whom a great portion of the year is darkness, who are condemned to pass weeks and months without the benign influence of the folar rays. The central folar ray is now perpendicular to the tropic of Capricorn; the length of the days is inversely what it was when the fun entered Cancer, the days being now at their shortest, and the nights longeft in the northern hemisphere; the length of each is pointed out by the horary index.

The earth being again carried on till it enters Libra, and the fun Aries, we fhall again have all the phenomena of the equinoctial feafons. The terminator will divide all the parallels into two equal parts; the poles will again be in the plane of the terminator; and confequently as the globe revolves, every place from pole to pole will defcribe an equal arch in the enlightened and obfcure hemifpheres, entering into and going out

of

of each exactly at fix o'clock, as fhewn by the hour index.

As the earth advances, more of the northern polar circle comes into the illuminated hemifphere, and confequently the days increase with us, while those on the other fide of the equator decrease, till the earth arrives at the first point of Capricorn, the place from which we first began to make our obfervations.

To explain the phenomena, that take place in what is called a parallel, dire&t, and right sphere.

Take off the globe and it's terminator, and put on in it's place the globe which accompanies the inftrument, and which is furnished with a meridian, horizon, and quadrant of altitude; the edge of the horizon is graduated from the east and weft, to the north and fouth points, and within these divifions are the points of the compass to the under fide of this horizon; but at 18 degrees from it another circle is affixed, to reprefent the twilight circle; the meridian is graduated like the meridian of a globe; the quadrant of altitude is divided into degrees, beginning at the zenith, and finishing at the horizon.

This globe, if the horizon be differently fet with refpect to the folar ray, will exhibit the various phenomena arifing from the fituation of the horizon with refpect to the fun, either in a right, a parallel, or an oblique fphere; or having fet the horizon to any place, you will fee by the central folar ray how long the fun is above or below the horizon of that place, and at what point of the compafs he rifes, his meridian altitude, and many other curious particulars, of which we fhall give a few examples.

Set

Set the horizon to coincide with the equator, and place the earth in the first point of Libra; then will the globe be in the pofition of a parallel fphere, and of the inhabitants of the poles at that feafon of the year, which inhabitants are reprefented by the pin at the upper part of the quadrant of altitude; the handle being turned round gently, the earth will revolve upon it's axis, and the folar ray will coincide with the horizon, without deviating in the leaft to the north or fouth; fhewing, that on the 21ft of March the fun does not appear to rife or fet to the terreftrial poles, but paffes round through all the points of the compafs, the plane of the horizon bifecting the fun's difk.

Now place the horizon, fo that it may coincide with the poles, and the pin reprefenting an inhabitant be over the equator, the globe in this pofition is faid to be in that of a right sphere; the. equator, and all the parallels of latitude, are at right angles, or perpendicular to the horizon; by turning the handle till the earth has completed a year, or one revolution about the fun, we shall perceive all the solar phenomena as they happen to an inhabitant of the equator, which are, I That the fun rifes at fix, and fets at fix, throughout the year, fo that the days and nights there are perpetually equal. 2. That on the 21st of March, and 22d of September, the fun is in the zenith, or exactly over the heads of the inhabitants. 3. That one half of the year between March and September, the fun is every day full north, and the other half between September and March, is full fouth of the equator, his meridian altitude being never lefs than 66 degrees.

If the pin reprefenting an inhabitant be now removed out of the equator, and fet upon any place between it and the poles, the horizon will not then pass through either of the poles, nor co

incide with the equator, but cut it obliquely, one half being above, the other half below the horizon; the globe in this ftate is faid to be in that of an oblique fphere, of which there are as many varieties as there are places between the equator and both poles. But one example will be fufficient & for whatever appearance happens to one place, the fame, as to kind, happens to every other place, differing only in degree, as the latitudes differ. Bring the pin, therefore, over London, then will the horizon reprefent the horizon of London, and in one revolution of the earth round the fun, we fhall have all the folar appearances through the four seasons clearly exhibited, as they really are in nature; that is, the earth ftanding at the first degree of Libra, and the fun then entering into Aries, the meridian turned to the folar ray, and the hour index fet to XII, you will then have the globe standing in the fame pofition towards the fun, as our earth does at noon on the 21st of March. If the handle be turned round, when the folar ray comes to the western edge of the horizon, the hour index will point VI, which fhews the time of fun-fetting; London then paffes into, and continues in darknefs, till the hour index having paffed over XII hours, comes again to VI, at which time the folar ray gains the eastern edge of the horizon, thereby defining the time of fun-rifing; fix hours afterwards the meridian again comes to the folar ray, and the hour index points to XII, thereby evidently demonftrating the equality of the day and night, when the fun is in the equinoctial. You may then alfo obferve, that the fun rifes due east, and fets due west.

Continuing to move the handle, you will find that the folar ray declines from the equator towards the north, and every day at noon upon the graduations of the meridian

rifes higher than it did

before,

before, continually approaching to London, the days at the fame time growing longer and longer, and the fun rifing and fetting more and more towards the north, till the 21ft of June, when the earth gets into the first degree of Capricorn, and the fun appears in the tropic of Cancer, rifing about 40 minutes paft 3 in the morning, and fetting about 20 minutes paft 8 in the evening, and after continuing about feven hours in the nether hemifphere, appears rifing in the north-eaft, as before. From the 21st of June to the 22d of September, the fun recedes to the fouth, and the days gradually decrease to the autumnal equinox, when they again become equal.

During the three fucceeding months, the fun continues to decline towards the fouth pole, till the 21st of December, when the fun enters the tropic of Capricorn, rifing on the fouth-eaft point of the compafs about 20 minutes paft 8 in the morning, and fetting about 40 minutes past 3 in the evening, at the fouth-weft point upon the horizon; after which, the fun continues in the dark hemifphere for 17 hours, and then appears again in the fouth-east, as before. From this chill folftice the fun returns towards the north, and the days continually increafe in length till the vernal equinox, when all things are reftored in the fame order as at the beginning.

Thus all the varieties of the feafons, the time of fun rifing and fetting, and at what point of the compafs; as alfo the meridian altitude and declination every day of the year, and duration of twilight, and to what place the fun is at any time vertical, are fully exemplified by this globe and it's apparatus.

Before we quit the phenomena particularly arifing from the motion and pofition of the earth, let the globe, with the meridian and horizon, be removed,