29

of the Solar Syftem.

the diameter M L will then be in the po-sition ml; lo that when the moon has de-scribed its orbit it will be at 1; but then thefun being at 8, the moon will not yet be inconjunction ; therefore the periodical monthis completed before the fynodical, and be-fore the moon can come into conjunctionwith the fun. When the earth is at D,fie must move from 1 to e, in the diameterg e ; whence, besides going round her or-bit, she must describe the arc 1 e, conse-quently the fynodical is longer than theperiodical month by the quantity of thearc 1 e.

61. We do not fee the moon at the con-junction, but at the opposition her wholedisc is enlightened.

In fig. 14. a T b represents a part of theearth’s orbit, 8 the fun, T the earth, ACEGthe moon’s orbit. If the moon is at A, itwill be on the fame side of the earth withthe fun, or in conjunction ; and the fun willthen be beyond the moon: therefore thefun does not shine on that hemisphere ofthe moon towards us; whence to us herwhole disc must be dark.

62. When