One of the 'handle bells' by Alexander Herschel, made as accessories for William Herschel's 40-inch telescope.

The substantial observing gallery of the 40-foot telescope's tube was raised and lowered to the appropriate height by ropes attached to either side of the gallery and passing over the top of the ladderwork and down to ‘compound barrels’, one on each side, turned by two workmen. The workmen would necessarily have to pull in unison, otherwise the gallery would tip over to one side, and to ensure this, each had a ‘handle bell’ that rang automatically once every time his handle was turned. These two ‘handle bells’ were of different pitch, so the workmen needed to hear the bells sound alternately to ensure the tube rose and lowered smoothly.

An example of the bells was illustrated in William's published description of the telescope. ZAA0887 is one of these, and it is provided with two hammers, one for each direction of winding, a peg on the handle-shaft (not surviving) lifting and dropping one hammer as it revolves in one direction and the other hammer on its return. The tails of the hammers are jointed so as to allow the actuating peg to pass by when returning.

During the 18th century, the role of the Royal Observatory was to produce tables to aid navigation. The work was routine and practical. Astronomical discoveries were left to amateurs such as the Herschels. William Herschel was originally a musician from Hanover but became interested in astronomy in 1773. In 1781 he spotted what he thought might be a comet using a seven-foot telescope. He immediately wrote to Nevil Maskelyne, then Astronomer Royal. The comet turned out to be the planet Uranus.

William Herschel was not only an amateur astronomer, he was also an instrument maker. In 1785 King George III gave William a grant of £2000 to build a 40-foot reflector telescope for William's own use (the remains of which are now on display at the Observatory). William also sold instruments to the Royal Observatory and to amateur astronomers.

William finished building his 40-foot Newtonian reflector telescope in 1789. It was the largest, most powerful telescope in the world and attracted visitors from far and wide. With it, William discovered the sixth and seventh satellites of Saturn and was able to resolve some globular clusters into individual stars.