This is the remaining 10ft of the speculum end of William Herschel's 40ft Herschelian (reflector) telescope tube. The remaining tube is made of iron and painted grey.

For 50 years, this telescope was the largest in the world. King George III granted £4000 for it to be made and between 1789-1840 it stood in the grounds of the Herschel's home, Observatory House, in Slough. As part of the deal he provided Caroline Herschel with a pension of £50 a year to act as William's assistant making her the first woman in England to be paid as an astronomer. Unfortunately, its huge size made it difficult to manage. Its one achievement was the discovery of the 6th and 7th moons of Saturn and even this is debatable (he used other telescopes at the same time).

The last observation made with the 40-ft telescope was in 1815.

John, William Herschel's son, dismantled the frame of the telescope in 1840 leaving the tube lying in the garden, 30 years later a falling tree crushed the tube leaving only this section.