The Astronomical Observatories of Jai Singh c7.7

c7.7

17. The characteristic part of the instrument is engraved on the reverse. The ordinary astrolabe was considered inconvenient, inasmuch as for every new latitude an additional tablet was required. Al-Zarqālī tried to remove this difficulty by substituting a horizontal projection for the usual polar projection. He took as his centre of projection one of the equinoctial points, and made the solstitial colure (i.e., the great circle passing through the solstitial points and the poles of the equator) the plane of projection.⁵