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1It is clearly by a divine and surprising arrangement, that the equinoctial gnomons are of different lengths in Athens, Alexandria, Rome, Piacenza, and in other parts of the earth. Hence the construction of dials varies according to the places in which they are to be erected; for from the size of the equinoctial shadow, are formed analemmata, by means of which the shadows of gnomons are adjusted to the situation of the place and the lines which mark the hours. By an analemma is meant a rule deduced from the sun’s course, and founded on observation of the increase of the shadow from the winter solstice, by means of which, with mechanical operations and the use of compasses, we arrive at an accurate knowledge of the true shape of the world.
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