228

Sir Isaac Newton ’s BookII.

geon is in conjunction with the fun, or in oppofition to it,and leaft of all when the apogeon is in the quarters.

yi. These changes in the nodes, in the inclination ofthe orbit to the plane of the earth’s motion, in the apogeon,and in the eccentricity, are varied like the other inequalitiesin the motion of the moon, by the different diftance of theearth from the fun; being greateft, when their caufe is great-eft, that is, when the earth is neareft to the fun.

y 3 . I faid at the beginning of this chapter, that Sir IsaacN e w t o n has computed the very quantity of many of themoon’s inequalities. That acceleration of the moon’s mo-tion, which is called the variation, when greateft, removesthe moon out of the place, in which it would otherwife befound, fomething more than half a degree a . In the phrafeof aftronomers, a degree is ~ part of the whole circuit ofthe moon or any planet. If the moon, without difturbancefrom the fun, would have defcribed a circle concentrical tothe earth, the fun will caufe the moon to approach nearerto the earth in the conjunction and oppofition, than in thequarters, nearly in the proportion of 6 y to 70 b . We hadoccafton to mention above, that the nodes perform their pe-riod in almoft 19 years. This the aftronomers found byobfervation ; and our author’s computations afiign to themthe fame period c . The inclination of the moon’s orbit whenleaft, is an angle about part of that angle, which conftitutes

J-Newt. Princ, Lib.III. prop.zp, B Ibid.prop. 28. ' Ibid. prop. 32.

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