ASTRONOMY.

135

With the first, it will make an angle of 1° 30';and with the second an angle of 5° 9'.

This curious fact was observed by Cassini. LaGrange has explained it from the theory of gra-vity.

Sect. VIII.

■ V.CI.1PSES OF THE SUN AND MOON.

137 . The Sun and Moon are both subject to oc-casional obscurations, most frequently partial, butsometimes also total, which are called Eclipses.

i 38 . The Eclipses of either of these luminarieshappen only when the moon is near her nodes;that is, either in the plane of the ecliptic or nearit. Those of the sun happen only at new moon, orwhen the moon is in conjunction with the sun :the eclipses of the moon, again, happen at the fullmoon, or when the moon is in opposition to thesun. The three bodies, then, the Sun, the Earth andMoon , are always nearly in the same straight linewhen an eclipse happens ; and conversely, whenthese three bodies are in a straight line, or not dis-

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