If the moon passed through the heavens in exactly the same path as the sun, there would result eclipses of both sun and moon at each revolution; for it would pass directly over the disc of the sun, and through the centre of the earth's umbra. But it was long since discovered that the path of the moon is inclined to the sun's path, or the ecliptic, about 5° (5° 8' 48"). This results from the fact that these crossing-places (which for convenience and according to astronomical usage we shall call the _nodes_), are in motion upon the ecliptic, from east to west. Therefore, the moon may cross the ecliptic at such a distance from the sun, that when it passes between the sun and the earth, it will appear to pass above or below the disc of the sun; also, in the opposite part of its orbit, it may cross at so great distance from the earth's umbra, that it will pass above or below the umbra, as represented in the following diagram. In June, the moon is seen below the sun, passing upward to the ascending node, and beyond the limits within which eclipses can occur. While the moon is completing another revolution around the earth, the sun continues to move eastward, and when it again comes to A the sun is near B. The moon, moving much faster than the sun, passes upward in its orbit, and is in conjunction with the sun at B, within the limits of eclipses. At this time the moon's umbra will fall upon the earth, and cause an eclipse, which will be total at all places over which the umbra will move; and partial at those places over which the penumbra will move. In this, as in all solar eclipses, only a part of the earth is covered by the shadows. [Illustration: _Limits within which Eclipses of the Sun can occur._] In August, at new moon, the sun has passed eastward to C, and the moon is seen above the sun, beyond the limit of eclipses. The following engraving is a projection of the shadows of the moon upon the earth, exhibiting that portion where a total eclipse will be visible; and those portions where a partial eclipse will be visible. [Illustration: _West._ _East._] As shown in the first cut, the shadows of the moon are of a conical form, and, if the total eclipse existed but an instant, its projection upon the earth would be of a circular form. But, since the earth revolves upon its axis, different parts are brought into the shadows; and this chart, to represent all that portion of the earth where any eclipse will be visible, has an oblong form. Also, since the sun appears to rise in one portion of the earth at the same instant when in another portion of the earth it appears to set, this projection exhibits those parts of the earth where the eclipse commences at the instant of sunrise and sunset. The next engraving is an enlarged representation of a part of the preceding; embracing a large portion of the United States, where a partial eclipse will be visible. [Illustration]