ABSTRACT
One of the greatest advances in exact astronomy, however, was the gradual adoption of principle of determining and correcting residual instrumental errors, instead of trying to reduce them to zero by continual adjustment of instrument. Neptune's mean distance was a severe blow to the empirical law of Bode above referred to being far too small to satisfy it. Uranus had fitted very badly, Neptune refused to fit at all. William Lassell, had made for himself a reflecting telescope, ingeniously arranged with an equatorial mounting and of such good definition that he discovered that Neptune had satellite, observations of which enabled planet's mass to be calculated. The mention of Lassell's equatorials which he did such good work, both near Liverpool and in Malta, brings us to other instrumental improvements of period. Abraham Sharp, who divided Flamsteed's great quadrant, Graham, with whose instruments Bradley made most of his observations, and Bird had brought art of graduating quadrants to high degree of accuracy.
