The Astronomical Observatories of Jai Singh c6.s1.t1.41

c6.s1.t1.41

² Figure 37 shows how the curve (i) is constructed for latitude 27 N. For each pair of signs, radii marking the angle of the meridian altitude of the sun are drawn, and the points of intersection of these radii with the corresponding arcs of the signs are joined. To make the graph perfectly correct, intermediate points must, of course, also be fixed. Figure 11 shows the unequal hour curves. According to Delambre (Astronomie du Moyen Age, p. 243) this is first described in a small work by Sacrobosco (circa A.D. 1250). It occurs on many old astrolabes, but it gives only roughly approximate results. To construct these hour lines the arc of the quadrant is divided into six equal parts and a semi-circle erected on one of the bounding radii. This is the sixth hour line and the others are arcs of circles of which the centres are on the same radius, but at points equidistant from the centre of the quadrant and from the successive points of division on the arc of the quadrant.