near enough to pass through the shadow of the earth. 363. An eclipse of the Moon takes place when the Sun, the Earth, and the Moon are in, or very nearly in, a straight line. 364. An eclipse of the Moon can take place only at the time of full moon. 365. On account of the inclination of the Moon's orbit to that of the Earth, an eclipse cannot take place every full moon. K 366. When the Moon passes entirely through the Earth's shadow, the eclipse is total; when only a part of it passes through the shadow, the eclipse is partial. 367. An eclipse of the Sun is occasioned by the Moon's coming directly between the Earth and the Sun, and thereby obstructing our view of the Sun. 368. When the Moon happens to be between the Sun and Earth at the time of new moon, there will be an eclipse of the Sun. 369. As the Moon is so much smaller than the Earth, only a small part of the Earth's surface can, at the same time, experience an eclipse of the Sun. 370. When any one of the heavenly bodies disappears by another body coming before it, it is called an occultation. 371. The occultations and approximations of the fixed stars by the Moon are of use in determining the longitudes of places. 97 OF THE TIDES. 372. The ebbing and flowing of the sea is owing to the attraction of the Sun and Moon, but chiefly to that of the Moon.. 373. This attraction cannot alter the shape of the solid parts of the Earth, but it has a great effect on the water, and causes it to assume a spheroidal figure, the longest axis. being in the direction of the Moon. 374. It is the highest tide at the place. which is perpendicularly under the Moon, or where the Moon crosses the meridian. 375. The tide is at its greatest height, not when the Moon is on the meridian, but some time afterwards; because the force by which the Moon raises the tide continues to act for some time after it has passed the meridian. 376. The oval figure of the waters keeps pace with the moon in its monthly journey round the Earth. 377. The Earth, by its daily rotation upon its axis, presents each part of its surface to the action of the Moon. 378. There are two tides in every place, in about 25 hours, because the action of the moon produces a tide in the place over which it passes, and also in the opposite surface of the globe at the same time. 379. When the action of the Sun and Moon conspire together, as at full and new moon, the tides are highest, and are called spring tides. 380. When they counteract each other, as in the quarters, they produce the lowest or neap tides.. ELECTRICITY. 381. The Earth and all the bodies with which we are acquainted are supposed to contain a certain quantity of an exceedingly subtle fluid, called the electric fluid. 382. The certain quantity belonging to all bodies is called their natural share, and produces no sensible effects. 383. When any body becomes possessed of more or less than its natural quantity, it is said to be electrified, and is capable of exhibiting certain appearances which are ascribed to the power of electricity. Example 1. Take a stick of sealing wax and rub it with your hand, or with a piece of flannel, or on your coat sleeve, and it will have the power of attracting small bits of paper or other very light substances when held near them. |