times exactly to the north pole of the heavens, which we have already described, and which is, as you recollect, within two degrees of the polar star in the diagram, page 14.

James. And how do you define the equator?

Tutor. The equator A B (in the last figure) is the circumference of an imaginary circle passing through the centre of the earth, perpendicular to the axis N s, and at equal distances from the poles.

Charles. And I think you told us, that if we conceived this circle extended every way to the fixed stars it would form the celestial equator.

Tutor. I did; it is also called the equinoctial, and you must not forget, that in this case it would cut the cir cle of the ecliptic C D in two points.

James. Why is the ecliptic marked on the terrestrial globe, since it is a circle peculiar to the heavens?

Tutor. Though the ecliptic be peculiar to the heavens, and the equator to the earth, yet they are both drawn on the terrestrial and celestial globes, in order, among other things, to show the position which these imaginary circles have in relation to one another.

I shall now conclude our present Conversation, with observing, that, besides the proofs adduced for the globular form of the earth, there are others equally conclusive, which will be better understood a few days hence.

CONVERSATION VII.

Of the Diurnal Motion of the Earth.

TUTOR. Well, gentlemen, are you satisfied that the earth on which you tread is a globular body and not a mere extended plane?

Charles. Admitting the facts which you mentioned yesterday, viz. that the top-mast of a ship at sea is always visible before the body of the vessel comes into sight;-that navigators have repeatedly, by keeping the same direction, sailed round the world;and that persons employed in digging canals, can only execute their work with effect, by allowing for the supposed globular shape of the earth, it

is evident the earth cannot be a mere extended plane.

James. But all these facts can be accounted for, upon the supposition that the earth is a globe, and therefore you conclude it is a globe: this was, I believe, the nature of the proof? Tutor. It was; let us now advance one step farther, and show you that this globe turns on an imaginary axis every twenty-four hours; and thereby causes the succession of day and night:

And earth self-balanc'd on her centre hung.
PAR. LOST.

James. I shall wonder if you are able to afford such satisfactory evidence of the daily motion of the earth, as of its globular form.

Tutor I trust, nevertheless, that

the arguments on this subject will be sufficiently convincing, and that before we part you will admit, that the apparent motion of the sun and stars is occasioned by the diurnal motion of the earth.

Charles. I shall be glad to hear how this can be proved; for if, in the morning, I look at the sun when rising, it appears in the east, at noon it has travelled to the south, and in the evening I see it in the western part of the heavens.

James.

Yes, and we observed the same last night (March the first) with respect to Arcturus, for about eight o'clock it had just risen in the north-west part of the horizon, and when we went to bed two hours after, it had ascended a good height in the heavens, evidently travelling towards the west.