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the motions of the celestial bodies which are more distant by 3500
miles when setting than when overhead, and yet do not increase or
diminish in any sensible degree.
8
71.
a b is the aperture through which the sun passes, and if you could
measure the size of the solar rays at n m, you could accurately
trace the real lines of the convergence of the solar rays, the
mirror being at a b, and then show the reflected rays at equal
angles to n m; but, as you want to have them at n m, take them
at the. inner side of the aperture at cd, where they maybe measured
at the spot where the solar rays fall. Then place your mirror at the
distance a b, making the rays d b, c a fall and then be
reflected at equal angles towards c d; and this is the best
method, but you must use this mirror always in the same month, and
the same day, and hour and instant, and this will be better than at
no fixed time because when the sun is at a certain distance it
produces a certain pyramid of rays.
8
72.
a, the side of the body in light and shade b, faces the whole
portion of the hemisphere bed e f, and does not face any part of
the darkness of the earth. And the same occurs at the point o;
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