JESSE

See also:

• JESSE RAMSDEN (1735-1800)

RAMSDEN (1735-1800)  , English astronomical instrument maker, was born at Salterhebble near Halifax, Yorkshire, on the 6th of October 1735 . After serving his apprenticeship with a cloth-worker in Halifax, he went in 1755 to London, where in 1758 he was apprenticed to a mathematical instrument maker . About four years afterwards he started business on his own account and secured a great reputation with his products . He died at Brighton on the 5th of November 1800 . Ramsden's speciality was divided circles, which began to supersede the quadrants in observatories towards the end of the 18th century . His most celebrated work was a 5-feet vertical circle, which was finished in -1789 and was used by G . Piazzi at Palermo in constructing his well-known catalogue of stars . He was the first to carry out in practice a method of reading off angles (first suggested in 1768 by the duke of Chaulnes) by measuring the distance of the index from the nearest division line by means of a micro-meter screw which moves one or two fine threads placed in the focu's of a microscope . Ramsden's transit instruments were the first which were illuminated through the hollow axis; the idea was suggested to him by Prof . Henry Ussher in Dublin . He published a Description of an Engine for dividing Mathematical Instruments in 1777 .