The Astronomical Observatories of Jai Singh c15.s3.5

c15.s3.5

The telescope was used for the general observation of heavenly bodies in 1609 by Galilei, and telescopic sights were first systematically used about A.D. 1667. Gascoigne was probably the first (circa A.D. 1640) to introduce these, and he also invented a micrometer. Some twenty years later, Huygens devised, independently, the same contrivance. Hevelius introduced the vernier and tangent screw; Flamsteed used cross wires in the eye pieces of his sighters; Galilei had used a pendulum for short time measurements; Huygens devised a pendulum clock (1656), and Jean Picard (1620-1682) introduced regular time observations at the new observatory at Paris.¹ J. D. Cassini (1625-1712), it is stated, devised schemes (never realised) for the construction of gigantic instruments.²