will be feen by them in constant rotation. As that half of the earth which is oppofed to the fun is always dark, the earth will exhibit the fame phases to the lunarians that we do to them, only in a contrary order, that when the moon is new to us, we fhall be full to them, and vice versa. But as one hemifphere only of the moon is ever turned towards us, it is only thofe that are in this hemifphere who can fee us; our earth will appear to them always in one place, or fixed in the fame part of the heavens; the lunarians in the oppofite hemifphere never fee our earth, nor do we ever view that part of the moon which they inhabit. The moon's apparent diurnal motion in the heavens is produced by the daily revolution of our earth.

If we confider the moon with respect to the fun, the inftrument fhews plainly that one half of her globe is always enlightened, by the fun; that every part of the lunar ball is turned to the fun, in the space of her monthly or periodical revolution; and that therefore the length of the day and night in the moon is always the fame, and equal to 14 of our days. When the fun fets to the lunarians in that hemifphere next the earth, the terreftrial moon rifes to them, and they can therefore never have any dark night; while thofe in the other hemifphere can have no light by night, but what the flars afford.

OF THE PERIODICAL AND SYNODICAL MONTH.

The difference between the periodical month, in which the moon exactly def:ribes the ecliptic, and the fynodical, or time between any two new moons, is here rendered very evident. To fhew this difference, obferve at any new moon her place

in the ecliptic, then turn the handle, and when the moon has got to the fame point in the ecliptic, you will fee that the dial fhews 27 days, and the moon has finished her periodic revolution. But the earth at the fame time having advanced in it's annual path about 27 degrees of the ecliptic, the moon will not have got round in a direct line with the fun, but will require 28 days and 4 hours more, to bring it into conjunction with the fun again.

OF ECLIPSES OF THE SUN AND MOON.

There is nothing in aftronomy more worthy of our contemplation, nor any thing more fublime in natural knowledge, than rightly to comprehend those fudden obfcurations of the heavenly bodies, that are termed eclipfes, and the accuracy with which they are now foretold. "One of the chief advantages derived by the prefent generation. from the improvement and diffufion of philofophy, is delivery from unneceffary terror, and exemption from falfe alarms. The unusual appearances, whether regular or accidental, which once spread confternation over ages of ignorance, are now the recreations of inquifitive fecurity. The fun is no more lamented when it is eclipfed, than when it fets; and meteors play their corufcations without prognoftic or prediction."

We have already obferved, that the fun is the only real luminary in the folar fyftem, and that none of the other planets emit any light but what they have received from the fun; that the hemifphere which is turned towards the fun is illuminated by his rays, while the other fide is involved in darkness, and projects a fhadow, which arifes from the luminous body.

When the fhadow of the earth falls upon the moon, it causes an eclipfe of the moon; when the fhadow of the moon falls upon the earth, it caufes an eclipfe of the fun.

An eclipfe of the moon, therefore, never happens but when the earth's opake body interposes between the fun and the moon, that is, at the full moon; and an eclipse of the fun never happens but when the moon comes in a line between the earth and the fun, that is, at the new

mioon.

From what we have already feen by the inftrument, it appears that the moon is once every month in conjunction, and once in oppofition; from hence it would appear, that there ought to be two eclipfes, one of the fun, the other of the moon, every month; but this is not the cafe, and for two reafons, firft, because the orbit of the moon is inclined in an angle of about 5 degrees to the plane of the ecliptic; and fecondly, becaufe the nodes of this orbit have a progreffive motion, which caufes them to change their place every lunation. Hence it often happens, that at the times of oppofition or conjunction the moon has fo much latitude, or what is the fame thing, is fo much below or above the plane of the ecliptic, that the light of the fun will in the first cafe reach the moon, without any obftacle, and in the other the earth; but as the nodes are not fixed, but run fucceffively through all the figns of the ecliptic, the moon is often, both at the times of conjunction and oppofition, in or very near the plane of the ecliptic; in thefe cafes an eclipfe happens, either of the fun or moon, according to her fituation. The whole of this is rendered clear by the lunarium, where the wire projecting from the earth, fhews when the moon is above, below, or even with the earth, at the times of conjunction

and

and oppofition, and thus when there will be, or not, any eclipfes.

The distance of the moon from the earth varies fenfibly with refpect to the fun; it does not move in a circular, but in an elliptic orbit round us, the earth being at one of the foci of this curve. The longer axis of the lunar orbit is not always directed to the fame point of the heavens, but has a movement of it's own, which is not to be confounded with that of the nodes; for the motion of the laft is contrary to the order of figns, but that of the line of apfides is in the fame direction, and returns to the fame point of the heavens in about nine years. This motion is illuftrated in the lunarium by means of the brafs ellipfis X Y, which is carried round the earth in little lefs than nine years; thus fhewing the fituation of the elliptical orbit of the moon, and the place of the apogee in the ecliptic.

OF A NEW TERRESTRIAL GLOBE,*

And of a new Apparatus adapted thereto, for folving, in an eafy and natural manner, the feveral Phenomena of the Sun, Moon, and Earth.

Though globes have ever been confidered as the best inftruments for conveying general ideas of aftronomy and geography, yet have they always been mounted in a way that nuft perplex and confufe the learner, and furnith him with ideas that are altogether falfe, and contrary to the nature of things.

The terreftrial globe was firft improved by my father, and placed in a fixed polition, &c, The floating meridian and horizon were added by Mr. Newman,

That you may clearly perceive the great advantages of a globe mounted like that before you, I fhall first point out a few of the imperfections of globes mounted in the common way, and how very unfit they are for the purposes of inftruction.

Now, in the first place, what is rectifying a globe thus mounted, but a continual abfurdity? for to rectify the globe to any particular latitude, the axis of the earth is continually shifted from one falfe pofition to another, the mind of the pupil is confufed, and he with difficulty conceives, that the axis of the earth never varies it's position, but always preferves the fame inclination to the plane of it's orbit.

The broad paper circle of the common globes is defigned to reprefent the ecliptic and the borizon but on examination you will find it reprefents neither the one nor the other. Now the ecliptic is the apparent path of the fun, to which the earth's axis always makes an angle of 66 degrees; now by fhifting the axis of the globe, to rectify for the latitude, this circle can never be in it's position as ecliptic, except when the axis is at 664 degrees, and confequently cannot be used as the ecliptic. Now let us confider it as the horizon. Now every place is always in the zenith of it's horizon, and the place and horizon always move together; but in the common globes the broad paper circle is only the horizon in one fituation, that is, when the place is in the zenith; after having rectified the globe to the latitude, the moment you move the globe, the broad paper circle is no longer the horizon. Thus is it plain, that this circle cannot with propriety be confidered either as horizon or ecliptic. As if it were to multiply confufion, a circle is laid down on the terrestrial globe to reprefent the ecliptic, and ufed as fuch in folving problems upon the

common