Page:On the connexion of the physical sciences (1834).djvu/28

16 lunar orbit, for example, is the point in which the moon rises above the plane of the ecliptic in going towards the north; and her descending node is that in which she sinks below the same plane in moving towards the south. The orbits of the recently discovered planets deviate more from the ecliptic than those of the ancient planets: that of Pallas, for instance, has an inclination of 35° to it; on which account it is more difficult to determine their motions. These little planets have no sensible effect in disturbing the rest, though their own motions are rendered very irregular by the proximity of Jupiter and Saturn.

The planets are subject to disturbances of two kinds, both resulting from the constant operation of their reciprocal attraction; one kind, depending upon their positions with regard to each other, begins from zero, increases to a maximum, decreases and becomes zero again, when the planets return to the same relative positions. In consequence of these, the disturbed planet is sometimes drawn away from the sun, sometimes brought nearer to him; at one time it is drawn above the plane of its orbit, at another time below it, according to the position of the disturbing body. All such changes, being accomplished in short periods, some in a few