S E -B W F with as many of the circles, as the shining of the sun will admit of, and the mean of all the bisecting lines, be chosen as a meridian, there will be no doubt of its accuracy, particularly if the observations be made about midsummer, which is the best time. In the preceding figure, NS represent the northern and southern points of the horizontal plane; if the line joining NS (the meridian line) be bisected at right angles, E will represent the eastern, and W the western points of the plane. So important, even in the early ages of astronomy, was the construction of a meridian line, that pillars were erected, on the shadows of which at noon, were marked the varying altitudes of the sun. A pillar of this kind was erected by Eratosthenes at Alexandria. Pliny also |
