![William Herschel's 40 foot telescope, also known as the Great Forty Foot telescope, was a reflecting telescope constructed between 1785 and 1789 at Observatory House in Slough, England. It used a 47 William Herschel's 40 foot telescope, also known as the Great Forty Foot telescope, was a reflecting telescope constructed between 1785 and 1789 at Observatory House in Slough, England. It used a 47](https://l450v.alamy.com/450v/2d8cy8r/william-herschels-40-foot-reflecting-telescope-copperplate-engraving-from-the-encyclopaedia-londinensis-or-universal-dictionary-of-arts-sciences-and-literature-volume-xvii-edited-by-wilkes-john-published-in-london-in-1820-2d8cy8r.jpg)
William Herschel's 40 foot telescope, also known as the Great Forty Foot telescope, was a reflecting telescope constructed between 1785 and 1789 at Observatory House in Slough, England. It used a 47
![Original mirror for William Herschel's 40 foot telescope, 1785. at Science and Society Picture Library Original mirror for William Herschel's 40 foot telescope, 1785. at Science and Society Picture Library](https://s3-eu-west-1.amazonaws.com/lowres-picturecabinet.com/43/main/51/130122.jpg)
Original mirror for William Herschel's 40 foot telescope, 1785. at Science and Society Picture Library
![William Herschel's 40 foot telescope at Slough, Berkshire, 1795. at Science and Society Picture Library William Herschel's 40 foot telescope at Slough, Berkshire, 1795. at Science and Society Picture Library](https://s3-eu-west-1.amazonaws.com/lowres-picturecabinet.com/43/main/3/82174.jpg)
William Herschel's 40 foot telescope at Slough, Berkshire, 1795. at Science and Society Picture Library
![William Herschel 40 Foot Telescope, 1880s Poster Print by Science Source - Item # VARSCIBU9002 - Posterazzi William Herschel 40 Foot Telescope, 1880s Poster Print by Science Source - Item # VARSCIBU9002 - Posterazzi](https://cdn11.bigcommerce.com/s-yzgoj/images/stencil/1280x1280/products/1490542/2021439/apiaxgpet__74171.1627199642.jpg?c=2)
William Herschel 40 Foot Telescope, 1880s Poster Print by Science Source - Item # VARSCIBU9002 - Posterazzi
![Sir William Herschel Great 40 foot telescope reflecting telescopes 1785 1789 Observatory House Slough England primary mirror Stock Photo - Alamy Sir William Herschel Great 40 foot telescope reflecting telescopes 1785 1789 Observatory House Slough England primary mirror Stock Photo - Alamy](https://c8.alamy.com/comp/C8NAJN/sir-william-herschel-great-40-foot-telescope-reflecting-telescopes-C8NAJN.jpg)
Sir William Herschel Great 40 foot telescope reflecting telescopes 1785 1789 Observatory House Slough England primary mirror Stock Photo - Alamy
![The Forty-Foot Telescope at Slough. Photographed by Sir John F.W. Herschel photographed 9 September 1839; this print made in August 1890 | Sir John Frederick William HERSCHEL The Forty-Foot Telescope at Slough. Photographed by Sir John F.W. Herschel photographed 9 September 1839; this print made in August 1890 | Sir John Frederick William HERSCHEL](https://www.jonathanahill.com/pictures/6384_2.jpg?v=1541600749)
The Forty-Foot Telescope at Slough. Photographed by Sir John F.W. Herschel photographed 9 September 1839; this print made in August 1890 | Sir John Frederick William HERSCHEL
![astronomy, instruments, the 40 foot telescope of William Herschel, wood engraving, 19th century, instrument, science, Great Britain, 18th century, historic, historical Stock Photo - Alamy astronomy, instruments, the 40 foot telescope of William Herschel, wood engraving, 19th century, instrument, science, Great Britain, 18th century, historic, historical Stock Photo - Alamy](https://c8.alamy.com/comp/B5M66D/astronomy-instruments-the-40-foot-telescope-of-william-herschel-wood-B5M66D.jpg)
astronomy, instruments, the 40 foot telescope of William Herschel, wood engraving, 19th century, instrument, science, Great Britain, 18th century, historic, historical Stock Photo - Alamy
![Herschel's 40 foot telescope, 19th Century illustration - Stock Image - C048/2017 - Science Photo Library Herschel's 40 foot telescope, 19th Century illustration - Stock Image - C048/2017 - Science Photo Library](https://media.sciencephoto.com/c0/48/20/17/c0482017-800px-wm.jpg)
Herschel's 40 foot telescope, 19th Century illustration - Stock Image - C048/2017 - Science Photo Library
![William Herschel's reflecting telescope of 40 ft (12 m) focal length, 1789 (1807). Artist: Unknown Stock Photo - Alamy William Herschel's reflecting telescope of 40 ft (12 m) focal length, 1789 (1807). Artist: Unknown Stock Photo - Alamy](https://c8.alamy.com/comp/AJA4RF/william-herschels-reflecting-telescope-of-40-ft-12-m-focal-length-AJA4RF.jpg)
William Herschel's reflecting telescope of 40 ft (12 m) focal length, 1789 (1807). Artist: Unknown Stock Photo - Alamy
![Astronomy: a 40-foot telescope constructed by William Herschel, in use outdoors. Coloured etching, 18--. | Wellcome Collection Astronomy: a 40-foot telescope constructed by William Herschel, in use outdoors. Coloured etching, 18--. | Wellcome Collection](https://iiif.wellcomecollection.org/image/V0024766/full/full/0/default.jpg)
Astronomy: a 40-foot telescope constructed by William Herschel, in use outdoors. Coloured etching, 18--. | Wellcome Collection
![William Herschel's Telescope, 1786-7. Sketch for engraving of 40 ft telescope presented to George III. William Herschel's Telescope, 1786-7. Sketch for engraving of 40 ft telescope presented to George III.](https://www.merlinprints.com.au/assets/full/arc14.jpg?20200714034054)