only a small part of the mast is visible to him, but as it advances, more of the ship is seen, till it arrive at e, when the whole will be in sight:

Behold, when the glad ship shoots from the port
Upon full sail, the hulk first disappears,
And then the lower, then the higher sails;
At length the summit of the towering mast
Alone is seen: nor less, when from the ship
The longing sailor's eye, in hope of shore:
For then, from the top mast, tho' more remote
Than either deck, the shore is first beheld.
LOFFT'S EUDOSIA.

Charles. When I stood by the sea-side the water did not appear to me to be curved.

Tutor. Perhaps not; but its convexity may be discovered upon any still water; as upon a river, which is extended a mile or two in length, for you might see a very small boat at that distance while standing upright; if then you stoop down so as to bring your eye near the water, you will find the surface of it rising in such a manner as to cover the boat, and intercept its view completely. Another proof of the globular figure of the earth is, that it is necessary for those who are employed in cutting canals, to make a certain allowance for the convexity; since the true level is not a straight line, but a curve which falls below it eight inches every mile.

Charles. I have heard of people sailing round the world, which is another proof, I imagine, of the globular figure of the earth.

Tutor. It is a well known fact that navigators have set out from a particular port, and by steering their course continually westward, have at length arrived at the same place from whence they first departed. Now had the earth been an extended plane, the longer they had travelled, the farther must they have been from home.

Charles. How is it known that they continued the same course? might they not have been driven round at open sea?

Tutor. By means of the mariner's compass, the history, property, and uses of which, I will explain very particularly in a future part of our lectures, the method of sailing on the ocean by one certain track, is as sure as travelling on the high London road from the metropolis of York. By this method, Ferdinand Magellan sailed in the year 1519 from the western coast of Spain, and continued his voyage in a westward course till he arrived after 1124 days in the same port from whence he set out. The same with respect to Great Britain, was done by our own countrymen Sir Francis Drake, Lord Anson, Captain Cook, and many others.

Charles. Is then the common terrestrial globe a just representation of the earth?

Tutor. It is, with this small difference, that

* What the earth loses of its sphericity, by mountains and valleys, is very inconsiderable: the highest mountain bearing

the artificial globe is a perfect sphere, whereas the earth is a spheroid, that is, in the shape of an orange, the diameter from pole to pole being about 37 miles shorter than that at the equator. James. What are the poles, sir?

Tutor. In the artificial globe (Plate v. Fig. 4.) there is an axis N s about which it turns; now the two extremities or ends of this axis N and s are called the poles.

The globe terrestrial, with its slanting poles,
And all its pond'rous load, unwearied rolls.

BLACKMORE.

Charles. Is there any axis belonging to the earth?

Tutor. No; but, as we shall to-morrow show, the earth turns round once in every 24 hours, so astronomers imagine an axis upon which it revolves as upon a centre, the extremities of which imaginary axis are the poles of the earth, of these N the north pole points at all times exactly

so little proportion to its bulk, as scarcely to be equivalent to the minutest protuberance on the surface of an orange:

These inequalities to us seem great;

But to an eye that comprehends the whole,
The tumour which to us so monstrous seems
Is as a grain of sparkling sand that clings
To the smooth surface of a sphere of glass:
Or as a fly upon the convex dome
Of a sublime, stupendous edifice.

LOFFT.

top, (Fig. 1.) the north pole of the heavens which we have already described, and which is, as you recollect, within two degrees of the polar star.

James. And how do you define the equator? Tutor. The equator A B (Fig. 4.) 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 equa

tor.

:

Tutor. I did it is also called the equinoctial, and you must not forget, that in this case it would cut the circle 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 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 XXVIII.

Of the Diurnal Motion of the Earth.

Tulor. 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 further, 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.