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These two stations are not on the same meridian, aswill he seen from fig. 7, Plate II., which shows CapeTown more than 18° of longitude east of Greenwich. *At present, however, we shall not take into accountthe difference of longitude.
Let fig. 8, Plate II., represent a side view of theearth at night, when Greenwich is at the place markedG. Let H h he a north and south horizontal line atGreenwich, G Z the vertical, G p (parallel to theearth’s polar axis) the polar axis of the heavens ; andlet us suppose that the moon, when crossing themeridian, is seen in the direction G M ; then theangle p G M is the moon’s north polar distance.
Again, let us suppose C to he the Cape TownObservatory, which has at the moment passed fromthe edge of the disc shown in fig. 8, hy nearly1 a hours’ rotation; but let us for the moment neglectthis, and suppose the station C to be at the edge ofthe disc. Let IP C h' be the north and south horizontalline at C, C Z' the vertical, C p' (parallel to the earth’spolar axis) the polar axis of the heavens (directednecessarily towards the south pole ); and let us sup-pose that the moon, when crossing the meridian, isseen in the direction C M'. Then, since the linesG M and C M' are both pointed towards the moon’scentre, they are not parallel lines, but meet, whenproduced, at that point.
Let fig. 9, Plate II., represent this state of things
* This figure is reduced from one of the four summer picturesforming Plate VII. of my “ Sun-views of the Earth .”