attracting body. The moon acts upon the solid and liquid parts at the same time; and in consequence of the mobility of the liquid parts, they are soonest and easiest drawn towards the moon, away from the solid parts of the earth; thus causing the waters of the ocean to be heaped up under the moon. This explanation accounts for one tide, only, during one revolution of the moon; and it is high water at two places upon the earth at the same time—one upon that part of the earth which is directly under the moon, and another upon the opposite side of the earth.

This second tide is explained in the following manner; the solid parts of the earth being nearer to the moon than the liquid parts, which are on the opposite side of the earth, are more attracted than the liquid parts; of course the solid parts are drawn away, and the waters will there rise. This explains the two high tides, and the low tides are a necessary consequence of the elevation; the two middle points between the two high tides, will have low tides at the time of high tide; so that there are two high tides and two low tides in about 24 hours, which is the moon's daily circuit round the earth.

As the earth turns on its axis once in about a lunar day, (and while she is so turning the moon is proceeding on her course about the earth, so that the earth must turn a little more than completely round before any place upon its surface will be in the same situation with respect to the moon that it was at the time of beginning the revolution,) this will cause any place to come to the meridian later, and thus cause high or low water at any particular place to happen about 50 minutes later on each succeeding day.

The orbit or path in which the moon moves about the earth, is but little different from the path in which the sun appears to move about the earth, (Ecliptic) and as this is in no place more than about 23 degrees from the equator, it is evident that the waters near the equator, being nearer to the moon than the poles, of course will be more attracted, and the tides at the equator will be higher than at the poles, where tides must disappear. The tides at the mouth of the river Amazon are very high, and extend more than five hundred miles up the river.

As the sun attracts the waters of the ocean, as well as the moon, when they both come into such a position as to act together, the tides must be higher than when but one of these bodies acts; but when the moon is at the full or change, they both act together, because then the sun, earth and moon are nearly in the same right line, and of course the tides will be higher at new and full moon-and they are then called spring tides. When the moon is in its quadratures, (quarters) the sun and moon act upon different parts of the earth at the same time, and each strives to raise a tide of its own, and therefore counteract each other's effect; this causes the waters not to rise so high as they otherwise would, and thus causes low tides, when the moon is in the quadratures, and these are called neap tides.

Most of our readers probably know, that all spring tides are not equally high; the nearer the sun and moon are to each other, the greater will be their combined action upon the waters of the ocean. Now the sun and moon are nearest together when the sun is in the equator, that is, at the time of the equinoxes (September and March.) But the sun is nearer to the earth at the fall equinox than at the spring equinox; therefore the action of the sun and moon upon the earth's waters will be greater at the fall equinox than in the spring; this causes the tides at or near the autumnal equinox (September 22d) to be higher than at any other time of the year.

The tides have a particular reference to the position of the moon, as well as to its phases; for it is always high water (in the ocean,) when the moon is on a particular point of the compass, (nearly S. W.) In theory it would seem to be high water at any particular place when the moon was south; but owing to the progressive effect of the moon's attraction, it is high water at some particular places about three hours before the moon comes to the meridian, while at others the high water comes after she has passed the meridian.

From accurate observations and registers of the phenomena of the tides, it is ascertained, that the highest tide during any one lunation, happens about one day and a half after the full or change. If the time of high water

happen at or near the same time of new or full moon, the third high tide after is found to be highest during the moon; this, correctly speaking, is the spring tide, there being but one during the moon. From the time of the highest tide during the moon, they gradually decrease until the third tide after the moon quarters, which is the lowest of all, and is properly the neap tide. After this the

tides again increase until the next spring tide and so on continually, the higher the flood tide rises, the lower the ebb sinks on that day. Thus we may observe, as in other cases, the effect of the sun and moon is not greatest, or least, when the immediate influence of the cause is greatest or least, as we see the greatest heat of the sun is not on the solsticial day, (when the sun is at its highest point) but some time after.

What has been said above, of the theory of the tides, must be understood upon the supposition, that the globe of the earth is entirely covered with water to a considerable depth; continents, which stop the course of the tides, straits between them, islands, and shallowness of the sea in some places, are all impediments to the course of the water, and thus cause many exceptions, which can only be explained from particular observations at different places. The latitude of the place appears to have considerable effect upon the tides; some phenomena happen in high latitudes which are not seen near the equator. If observations upon the tide are made at a place which has the same latitude as the moon has declination, (distance from the heavenly equator) but a single tide will be seen, there being 12 hours of flood and 12 hours of ebb.

We have said that local circumstances greatly modify all the phenomena of the tides: the following are illustra tions of this remark. The position of shores, the width of channels through which the waters pass, the extent of seas, direction of prevailing winds with respect to the shores, &c. all have considerable influence upon the quantity of the tides. Strong winds, in a particular direction for a long time, produce currents in the ocean, which of course will affect the tides; this will cause places subject to the same influence of the sun and moon to have very different tides, Continents stop the tides in their

course from east to west; therefore the tides on an eastern coast are higher than on a western the waters of the Mexican Gulf, on the eastern coast of America, are several feet higher than the waters of the Pacific ocean, on the western side of the Isthmus of Darien. The waters of the Red Sea are a number of feet higher than those of the Mediterranean. Rivers and bays opening to the east, have higher tides than those with a western aspect; in such places the tides are further influenced by the adjacent shores. Where bays have a narrow entrance or are narrow in their course, tides often rise to a great height. In the Bay of Fundy the tides often rise sixty feet, and with great rapidity; the tides also are very high in the strait of Sunda, and in the Red Sea; all of these have an eastern aspect. But in the Baltic sea, and in the Mediterranean, there is but very little tide, as their entrance opens to the west. This fact probably explains the reason why the ancients were ignorant of any such phenomena as the tides. Narrow channels oppose so much resistance to the water, that tides in such places often rise with astonishing rapidity; in some of the rivers on the eastern coast of England, the flood tides enter them with a head of several feet; that is, the waters of the coming tide are several feet above the waters of the river. In some situations, where there are great obstructions, and a crooked course for the tide to follow, there are several tides at the same time, but a short distance from each other; as, it is high water at London and at the mouth of the Thames at the same time, while between, it is low tide. In the river Amazon in South America, there are no less than seven high tides at the same time, while there is a low tide between every two. It would be endless to specify all the circumstances applicable to particular cases, as the solutions are easy consequences from the general statement of the facts above given. We shall dwell but a moment longer on this part of our subject. Why do not lakes and large inland seas, as Lake Superior, the Caspian sea, &c. have tides? The reason is, lakes are so small, compared with the ocean, that where the moon is vertical, (or south) she attracts every part of a lake alike, so that no part of the water can be raised above another; and having no communication with the

ocean, it cannot increase or diminish the quantity of water so as to make it rise or fall. The same reason will apply where large bodies of water are connected by narrow channels with the ocean; they are so large, and their inlets so narrow, that they cannot readily receive water enough to raise their surfaces.

ECLIPSES O F THE MOON.

All the planets of our system, and their satellites, are illuminated by the sun; it is his light which makes them visible to the inhabitants of the earth; it is evident then, that all of these cast shadows towards that point of the heavens which is opposite to the sun.

The light of the sun makes the surface of the moon visible to us upon the earth, and if the earth or any other opaque body should come between the sun and moon, it would cast a shadow towards the moon, which of course, if long enough, would intercept a part or the whole of the sun upon the moon, and thus cause an eclipse of the moon. When the moon is eclipsed to us, a spectator at the moon would of course see an eclipse of the sun, which would be total to those parts on which the shadow of the earth fell.

An eclipse of the moon happens only at the time of full moon, because then only the earth is directly between the sun and moon. There is not an eclipse of the moon at every full, as there would be if the sun, earth, and moon were then in the same right line. To explain the cause of eclipses of the moon, we invite those who are not ready in conceiving the subject, to make use of the following simple contrivance to render palpable this part of our subject. Take two pieces of common wire of unequal lengths, say of four and two feet; make these into circles, and let each one have two supports-the supports for the larger circle of equal lengths, say about one foot, the supports for the smaller circle one 93 inches, and the other 14 inches, or in this proportion. Let the wire circles be placed upon these supports so as to divide each circle into two equal parts, and place them upon a table, the small circle within the larger; and then place one of the balls, mentioned in a former illustration, in the middle