For then, from the top-mast, tho' more remote LOFFT'S EUDOSIA. Charles. When I stood by the seaside 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 in the first 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, properties, 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 nearly as sure as travelling on the high London road from the metropolis to 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 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 87 miles shorter than that at the equator. The globe terrestrial, with its slanting poles, And all its pond'rous load, unwearied rolls. BLACKMORE. * What the earth loses of its sphericity, by mountains and valleys, is very inconsiderable; the highest mountain bearing 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; Or as a fly upon the convex dome LOFFT. James. What are the poles, sir? Tutor. In a the artificial globe there is M HA an axis NS about which it turns; now the two extre mities or ends of this axis N and s are called the poles. 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 |