light from the Sun. So whenever the Moon passes between the Earth and the Sun, in such a manner as to hinder the rays of the latter from falling on the Earth, then will the Sun be eclipsed to the inhabitants of the Earth: and whenever the Moon passes behind the Earth so as to hinder the rays of the Sun from falling on the Moon, then will the Moon be eclipsed to the inhabitants of the Earth. An Eclipse of the Sun can only happen at the Change of the Moon, when the Moon is between the Sun and the Earth; and an Eclipse of the Moon can only happen at the Full of the Moon, when the Earth is between the Sun and Moon. This will be evident by referring to the positions of the Sun, Moon, and Earth during the full and change, as exhibited in fig. 6 of Plate II. : 48. The orbit of the Moon crosses the Ecliptic so as to make an angle of five degrees' inclination, and these points of intersection are called the Nodes of the Moon, being distinguished from each other as the ascending and descending the ascending node is where the Moon ascends Northward above the ecliptic, and the descending node, where she descends Southward below the ecliptic; they are both marked in Plate II. fig. 7. Now, these Nodes, being the only two points where the Moon crosses the Ecliptic, hence, there can be no Eclipse of the Sun but when she changes in, or near, one of the Nodes, because then only she comes so between the Earth and Sun, as to intercept the rays of the latter from the Earth and in like manner, there can be no eclipse of the Moon but when she is full in, or near, one of the Nodes, because then only the Earth comes so between her and the Sun, as to hinder the rays of the latter from falling on her. This is the reason why there is not an Eclipse of the Sun at every change of the Moon, and an Eclipse of the Moon at every full of the Moon. 49. The Shadows cast by the Earth and Moon are of a conical figure (as may be seen in fig. 7), growing narrower and narrower the farther they go from the Earth and Moon, until at last they end in a point, and so cease. This is owing to the Earth and Moon being smaller bodies than the Sun : were they the same size as the Sun, it is evident that the shadows must be cylindrical (as in fig. 8), and were they larger than the Sun, the shadows would be like inverted cones (as in fig. 9). And hence, in consequence of the Earth being much bigger than the Moon, the cone of its shadow is great enough to intercept the Sun's rays from the whole of the Moon's surface at one time: whilst, on the other hand, the Moon being smaller than the Earth, can intercept the Sun's rays only from a small part of the Earth at one time'. 1 Herein too, the much greater distance of the orbit of Mars becomes evident; for, though the Earth may be directly between the Sun and Mars, yet is the latter not eclipsed, as it must necessarily be, did the shade of the Earth reach to its orbit. The Shadows of the Earth and Moon being thus of a conical figure, it is ob vious, that an Eclipse of the Sun or Moon will be greatest or longest when the Moon is in her Perigee, or nearest the Earth; for then she has to traversé a thicker part of the Earth's shadow, than when eclipsed in her Apogee or greatest distance from the Earth. This may be seen in fig. 7, where P P denotes the breadth of the Earth's shadow traversed by the Moon in her Perigee, and A A so much of it, as is traversed by her when in her Apogee, And, in like manner, if the Sun be eclipsed when the Moon is in her Perigee, it meets with a thicker part of the Moon's shade than it does when she is in her Apogee; as may be also seen in fig. 7, by supposing T to be the Moon, PP her shadow traversed by the Earth when she is in her Perigee, and A A her shadow traversed by the Earth when she is in her Apogee. 50. But the Greatness and Duration of an Eclipse arise principally from the Moon's being then more, or less, distant from a Node. An ECLIPSE OF THE MOON is either Total, that is when the whole of her is eclipsed, or Partial when only a part of her is eclipsed: and as some partial eclipses are of longer duration than others, so some total eclipses are likewise of longer duration than others. Now, those Total Eclipses which are of the longest, duration, happen when the Moon is exactly in a Node; they are called Central Eclipses, from the centre of the Moon passing through the centre of the Earth's shadow. This is illustrated in fig. 10 of Plate II., where the shaded circle represents the Earth's shadow, O M the Moon's orbit, and E C the Ecliptic: whence it is evident, that the Moon crossing the Earth's shadow in a diametrical direction, makes the longest possible stay she ever can make in it; this stay is about four hours long, the breadth of the Earth's shade being about three diameters of the Moon. 51. A Total, but not Central, Eclipse is represented in fig. 11, where the Moon meets the Earth's shadow at a small distance from a Node, and so' crosses only a Chord (or portion) of the Earth's shadow, and not its diameter: whence likewise, it is evident, that this chord will be greater or smaller, according as the Moon is nearer to, or farther from, a Node, and that the duration of every Total Eclipse will necessarily depend on the length of this. chord. Hence also it follows, that some Eclipses are more Partial than others, according as the Moon is at a greater, or less distance from a Node; and that the longer a Partial Eclipse is, so much more of the Moon passes through the shadow of the Earth. A Partial Eclipse is represented in fig. 12, where it will be seen, that the Node is at some distance from the centre of the Earth's shadow, and that, consequently, the Moon traverses so small a chord of this shadow, that the whole of her surface is not darkened. In order to distinguish the greatness of Partial Eclipses, it is usual to conceive the Moon's diameter as divided into twelve parts, called Digits; and to say, there are so many digits eclipsed, as there are such parts covered by the Earth's shadow, when the Eclipse is at the greatest. In all these Eclipses of the Moon, she enters the Western side of the shadow with her Eastern side and so it is her Western side, which quits the shadow when the Eclipse ceases. 52. ECLIPSES OF THE SUN are also distinguished as Total, that is, when the Moon covers the whole body of the Sun from us, and as Partial, when she covers only a part of the Sun. When there is a Total Eclipse of the Sun it is so dark, that the Stars appear very visible, and there is even need of lamp-light; but, this total darkness, even under the most favourable circum stances, never lasts more than about five minutes; for, as soon as a very small part of the Sun's disc becomes uncovered, it affords us considerable light. But it has been already observed, that although the Earth can eclipse the whole enlightened hemisphere of the Moon, and so involve the whole of her body in darkness at the same time; yet, that the Moon (in consequence of her being so much smaller than the Earth) can never obscure more than a small part of the Earth at the same time. This will be seen by referring to fig. 13 of Plate II., where the Moon's shadow only covers a small part of the illuminated surface of the Earth, (viz. that between C. and D), so as totally to hide the Sun's rays from it; whilst, to the inhabitants of the adjoining tracts B C and D E, the Sun will appear to be but partially eclipsed; and, beyond this last (as is evident from the figure) there will be no eclipse of him at all. 53. It happens sometimes, that a Central eclipse of the Sun is not a Total eclipse, but that there is a ring, or circle of light all round the edge of the Moon (as in fig. 14), wherefore, such an eclipse is said to be annular. This annular appearance is occasioned by the conical shadow of the Moon being too short to reach quite to the Earth, owing to the Moon being in her Apogee: it may be better understood by referring to Plate II. fig. 7, and supposing S to represent the Sun, T the Moon and E the Earth.-In the greatest eclipses of the Sun, the Moon's shadow passes along the middle of the Earth; and such eclipses happen when the Moon is in a Node at the moment of her Change. If she be not too far from a Node, a part of her shadow will fall on some tract of the Earth, and there make a Total, or, at least, a Partial eclipse; and, in proportion as she is nearer to her Node and her Perigee; will be the greatness and length of the obscuration. 54. THE TIDES are caused chiefly by the attraction of the Moon, but partly by that of the Sun. The Sea flows (i. e. rises) as often as the Moon passes the meridian, both the arc above, and the arc below, the horizon; and it ebbs (i. e. falls) as often as she passes the horizon, both East and West. When the Moon is in the first, and third, quarters (i. e. when she is new and full), the tides are high and swift, and are called spring-tides; when she is in the second, and last, quarters (i. e. when she is a half-moon), the tides are lower and slower, and are called neap-tides. 55. But the lowest, as well as the highest water, will be found at the spring-tides; the neap-tides neither rising so high, nor falling so low: those spring-tides which happen at the time of the equinoxes, and whilst the Moon is in her Perigee, are always the highest. The Sea is observed to swell and flow from South to North for about six hours, after which it seems to rest for about a quarter of an hour; it then begins to fall and retire back again from North to South for six hours more, when, after an apparent pause of a quarter of an hour, it begins to flow again as before. Thus the sea flows and ebbs alternately twice a day, but not at the same hours; for the tides return later and later every day by 50 minutes, which is the excess of a lunar day above a solar one. 56. Though the action of the Moon has the greatest share in producing the tides, yet the action of the Sun adds sensibly to it when they unite their forces together, as is the case at the full and change of the Moon, when they are nearly in the same line, with the centre of the Earth. Thus, at the change, when they are both on the same side of the Earth, they both conspire to raise the water in the zenith, and, consequently, in the nadir; but, when the Moon is at the full, and the Earth is between her and the Sun, one causes high water in the zenith and nadir, whilst the other does the same in the nadir and zenith: consequently, these are the highest tides, and are what are called Spring-tides. Farther, the action of the Sun diminishes the effect of the Moon's action in the first and last quarters, because the one raises the water whilst the other depresses it; then, therefore, the tides are the least, and are called the neap-tides. But it must be observed, that the spring-tides do not happen precisely at new and full moon, nor the neap-tides at the quadratures, but a day or so afterwards; because, as in other cases, so in this, the effect is not greatest or least, when the immediate influence of the cause is greatest or least. This may be also observed with respect to the greatest heat and cold, which are not felt on the Solstitial days, when the action of the Sun is greatest and least. The tides rise to different heights in different parts of the world; in the Bristol Channel they rise above forty, feet, and on the Eastern coast of North America more than fifty feet; but their average height is considerably under twenty feet. CHAPTER II. THE WORLD. 1. GEOGRAPHY is that Science which teaches the knowledge of the Earth; it derives its name from the Greek words yn the earth, and ypápw to describe. 2. According to its strict etymology, Geography denotes the description of the Earth only, and is thus distinguished from Hydrography, which refers to the description of the Sea, or Water (vdwp); but, as earth and sea are usually considered by Geographers, as the great component parts of the Terraqueous Globe, hence, the description of them both is generally included in the term Geography. In either of these senses, it differs from Cosmography, which is a description of the Universe (xóoμoç), as a part differs from the whole; and also from Chorography, which is the description of a country (xwpa), and from Topography, which is the description of a place (rónog), as the whole differs from a part. 3. The situation of places is determined as to North or South by their latitude, and as to East or West by their longitude; and these distances are reckoned in degrees and minutes. Every circle, whatever may be its diameter, is divided into 360 degrees; this arose from the ancients supposing that the great circle in the heavens, called the Ecliptic, was traversed by the Sun in 360 days, and hence, they named each day's progress, which he made along this circle, a gradus, step or degree. Each Degree is subdivided into 60 minutes (or miles), and each minute into 60 Seconds, and these are denoted by the signs,, "; thus 51°. 30. 45" means 51 degrees, 30 minutes, 45 seconds: moreover, N stands for North, and S. for South, Latitude; E. for East, and W. for West, Longitude. 4. The Latitude of a place is its nearest distance from the Equator, either North or South; when the place is North of the Equator it is said to be in North Latitude, when South of the Equator it is in South Latitude. And, because the Equator divides the Earth into two equal parts, which again are divided by the Axis of the Earth into two other equal parts, therefore, the whole great Meridian circle of the Earth is divided into four equal parts: and, as every circle contains 360 degrees, therefore, a fourth part of a circle can contain only 90 degrees. Hence it follows, that Latitude, which is the distance of a place from the Equator, either towards the North, or South, Pole, can never exceed 90 degrees; and, that every line of Latitude, inasmuch as it remains always parallel to the Equator, is therefore called a Parallel: thus we say the parallel of London, the parallel of Rhodes, &c. meaning to say, the line of latitude which runs through London, or Rhodes. Places situated on the Equator itself are said to have no latitude. 5. The Longitude of a place is its distance from a given spot, due East or West, and is measured either on |