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of the Solar System.

secondary, passing through it, if it couldbe viewed from the earth’s center, so as toappear at Y ; when at R, its latitude is R O,when at'Y, its latitude is QY, the diffe-rence N Y, is the parallax of latitude.

78.When the planet appears at R in PRO,the secondary of the ecliptic, the point Ois its longitude from the first point of Aries;but when at Y in the secondary PYQ,Q_js the point of its longitude; whencethe difference Q^O is the parallax of lon-gitude.

But if the planet be in a vertical circleZ W, which passes through P, the pole ofthe ecliptic, it can only have a parallax oflatitude, and none of longitude. Let abbe the parallax of latitude ; whence fromeither station, ab will be its parallax of lati-tude ; and as there can pass but one se-condary through both, there can be noparallax of longitude.

The annual parallax of any heavenly bodyarises from its being seen from the earth,when it is in different parts of its orbit.

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