that arise from his fituation, by which he is forced to confider them from a point which is not in the center of the fyftem, and is confequently the fource of many apparent irregularities. It will then alfo be easy to prove to him, that the real and apparent motions of the heavenly bodies are frequently the reverfe of each other. For being by this means put into poffeffion of the univerfals of this fcience, the knowledge of particulars will be rendered facile and clear.

OF THE SOLAR SYSTEM, AS SEEN BY A SPECTATOR, SUPPOSED ΤΟ BE PLACED IN THE SUN.

As the center of the fyftem is the only place from which the motion of the planets can be truly seen, let us suppose our observer placed at the center of the fun. In this fituation he will fee at one view all the heavens, which will appear to him perfectly spherical, and the stars as fo many lucid points in the concave furface of the sphere; the center of which is the fun, or, in the present instance, the eye of the observer.

Our spectator will not, however, immediately conclude from appearances, either that the heavens are really spherical, or that the fun is in the

center of the sphere, or that the stars are all at an equal distance from him; having been taught by experience and observation, that while he remains in the fame place, he cannot judge properly of the distance of furrounding objects, at least of those which are placed beyond the ordinary reach of his view: for beyond that distance, all the principles by which we form our general judgment fail us, and we can only tell which is nearest, or which is furtheft, either by our own motion, or that of the objects,

To illuftrate this, let us fuppofe a number of lamps, to be placed irregularly, at different distances from the eye, in a dark night. Now as in this cafe, we fuppofe the darkness to be fo complete, that no intermediate objects could be feen, no difference in colour discerned, nor any perception of a convergence towards the point of fight, our judgment could not affift us in diftinguishing the distance of one from the other, and they would therefore all feem to be at an equal distance from the spectator.

For the fame reafon, the fun and moon, the stars and planets, appear to be all at an equal distance from us; though it is highly probable, that fome of the ftars are many millions of times

nearer

nearer to us than others. The fun is demonftrated to be nearer than any of the ftars. The moon and some of the planets are known by ocular proof to be nearer to us than the fun, because they fometimes come between it and our eye, and hide the whole, or a great part of his disk, from our view. They all, however, appear equally diftant, and to be placed in the furface of a fphere, whereof our eye is the center. In whatever place, therefore, the fpectator refides, whether it be on this earth, in the fun, or in the regions of Saturn, he will confider that place as the middle point of the universe, and as the center of the world; for it will be to him the center of that spherical furface, in which all diftant bodies appear to be placed.

Here the tutor will find his advantage in illuftrating this fubject, and extending the ideas. of his pupil, by actual experiments on real objects. Young people fhould be taught to gain as much information as poffible from fenfible images; by these their mind would be gradually led to feel it's powers, and foon learn to correct those errors which are induced into it by appearances, derived only from the fenses. No man can at once convey light in the higher subjects to another man's understanding. It must come

into the mind from it's own motions, within. itfelf; and the grand art of philosophy and education, is to set the mind in action, and even when we think nothing of it, to affift it in it's labour.*

The pupil may now proceed to confider the obfervations of the solar spectator; to whom, as we have already obferved, the heavens will appear as the furface of a concave sphere, concentrical to his eye in this furface he will difcover an innumerable hoft of fixed ftars, which will for fome time engage his attention, before he difcovers that they may be distinguished into two kinds; the one difperfed through the whole heavens, differing in their degree of brightness, but remaining always at the fame relative distance from each other. These he will therefore call FIXED STARS, or only STARS. Befides thefe, he will find fome others moving among the foregoing with different velocities, which he will call WANDERING STARS, or PLANETS.

Here, however, it may be proper to obferve, that what we call the fky, in which the heavenly bodies feem as it were to be fixed, is no real fubftance.

5

*Petvin's Notes to Letters on Mind.

fubftance. If there was no atmosphere surrounding our earth, whofe particles might reflect other rays of light to our eyes, than thofe which come directly from the fun, all parts of the heavens, even at mid-day, would be dark, and the ftars be vifible at noon. But, as our atmosphere abounds with particles capable of reflecting light every way, fome of it will fall upon our eyes whitherfoever they are directed; from the nature of this reflection, we receive the idea of colour, and the mind immediately imagines a substance wherein it may refide; in the fame manner, the regular reflection of light from an object in a looking glafs, is combined by the mind into an image of that object.

Mr. de Sauffure, when on the top of Mount Blanc, in Savoy, a mountain which is elevated 15673 feet perpendicularly above the sea, and where confequently the atmosphere must be much rarer than our's, fays, that the moon fhone with the brighteft fplendor in the midst of a sky as black as ebony; while Jupiter, rayed like the fun, rofe from behind the mountains in the eaft.*

*

Appendix to vol. 74, Monthly Review.

OF