The telescope was constructed by Sir William Herschel, with the assistance of his sister Caroline Herschel,
between 1785 and 1789 in Slough, with components made in Clay Hall near Windsor.
The 40 ft (12 m) tube was made of iron.
The telescope was mounted on a fully rotatable alt-azimuth mount.
It was paid for by King George III, who granted £4,000 for it to be made.