Original mirror for William Herschel's forty-foot telescope, 1785.

Made:: 1785 in England, Slough and Maidenhead

maker:: William Herschel

The first 48-inch speculum mirror cast with metal cover by Sir William Herschel in 1785 for his 'Forty Foot' telescope at Slough, England.

The astronomer, Sir William Herschel made this 48-inch concave metal mirror for his '40-Foot Telescope' at Slough, England. Cast in 1785, the mirror is made of speculum, a bronze alloy with arsenic for a more lustrous finish. Weighing only half a ton, the mirror proved to be too thin to hold its shape properly once it had been ground and polished to its final form. A few years later, a heavier second mirror was cast which was used in preference to the original one. Completed in 1787, Herschel's great telescope soon became a wonder of the age. It quickly became a landmark of Slough visited by the rich and famous visiting the king at nearby Windsor.

Details

Category:: Astronomy

Object Number:: 1932-567

Materials:: complete, speculum (alloy of copper and tin) and iron

Measurements:: overall (including ring): 150 x 1260 x 1260 mm

type:: components, concave mirrors, metal mirrors and astronomical instruments

credit:: Revd Sir John Charles William Herschel

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Original mirror for William Herschel's forty-foot telescope, 1785.

The first 48-inch speculum mirror cast by Sir William Herschel in 1785 for his 'Forty-Foot' telescope at Slough, England.

The astronomer William Herschel made this 48-inch concave metal mirror for his '40-Foot Telescope' at Slough, England. Cast in 1785, the mirror is made of speculum, a bronze alloy with arsenic for a more lustrous finish. Weighing only half a ton, the mirror proved to be too thin to hold its shape properly once it had been ground and polished to its final form. A few years later, a heavier second mirror was cast which was used in preference to the original one. Completed in 1787, Herschel's great telescope soon became a wonder of the age. It quickly became a landmark of Slough visited by the rich and famous visiting the king at nearby Windsor.