Puslapio vaizdai
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One of the strongest arguments for the rapid rotation of Jupiter (befide actual obfervation), is his fhape; which differs in measure between his poles, and at his equator, as, 12 to 13.

As to the heights of mountains or depths of vallies, they are not equal to the roughneffes on the furface of an orange; which yet nobody fcruples to call round.

If the earth is round, there must be fome places whose inhabitants are our ANTIPODES, i. e. whofe feet are oppofite to ours; for every place must have its Antipodes; fince all points on the surface of a globe, muft have oppofite points: otherwife it implies chafms and breaches. It follows also, that at antipodial (or exactly oppofite) meridians of the globe, the parts of the day are contrary: morning to one, evening to the other; noon to one, night to the other. The feasons alfo are contrary in contrary latitudes, as already explained.

Thus have we noticed the principal particulars of our earth confidered as a planet. Is there not much pleasure accompanying fuch enlarged views of its general properties! In confidering all men as brethren, however diftinguished by various climates, or feparated by local distances! O that the general viciffitudes of light and darkness, of heat and cold, of sunfhine and clouds, of fair weather and tempefts, might promote equally general fentiments of humanity among mankind!

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OBSERVATIONS ON THE PLATES

Belonging to LECTURE

VII.

PLATE I. SHAPE OF THE EARTH.

FIG

IG. 1. and 2. These figures are examples of the application of the principle adduced in the Lecture, p. 147. A fig. 1. represents a ship failing from the Tower B. It appears clearly, that the lower parts both of the tower and ship are first concealed by the rot undity of the circle; and are totally invisible, while the mafts of the ship and the battlements of the tower are yet difcernible. Agreeable to this idea, the figure C fees only the maft of the distant veffel E coming to him, while he fees diftinctly the whole of D, which is nearer.

Fig 2. reprefents the fame effect in fhips advancing to land. A cannot as yet fee any part of the mountain C, it being concealed by the circumference of the earth: while B enjoys a full view of it; the vifual ray paffing clearly over the earth's circumference.

Fig. 3. HORIZON. This fig. fhews that the fenfible horizon (i. e. what part of the earth's furface actually bounds our view) is juftly confidered as coincident with the rational, or celeftial horizon HO: for though to the figure A there

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is great difference between an object placed at 1, on the true horizon, and another at a or b on his apparent horizon; yet this difference is perpetually decreasing, as the distances of objects increase. The object C at the distance 2, being feen from E much nearer 1. The object D at the distance 3 nearer ftill to 1. The object b or o, at H and O nearer ftill. It is but adding yet further distances, and the spaces on the line a, c, d, b, 1, will approach nearer and nearer, till at length they become totally infenfible: So that with regard to objects at very remote ftations, A and E will have precisely the fame horizon.

Z being vertical to A is the Zenith, N being centrically under him is Nadir.

In conformity to this principle, it is ufual to calculate all appearances of the heavenly bodies as if they were viewed from the centre of the earth, and there were no diftance from the centre to the circumference: [i. e. that the earth were a point only.] For though to its inhabitants this globe be large and capacious, yet when compared to space around it, it shrinks into nothing. Therefore when the fun is faid (or reprefented) to be in any ftation, we must take with us the idea of his being fo as feen from the centre of the globe. The fame of the planets: though in nice obfervations, the diameter of the earth has its effect; and comes under the principles of PARALLAX (efpecially with regard to the moon), and is one way of calculating their distances, and fizes.

PLATE

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