Photographic print of William Herschel's 40-foot telescope at Slough, in frame made from mahogany ladder rungs from the mounting of the 20-foot telescope used at Slough by William and at the Cape by John Herschel. Printed in 1890, one of 25 prints made from the first permanent negative taken by Sir John F.W. Herschel in 1839.

This image shows the only photograph ever taken of William Herschel's 40-foot telescope at Slough just prior to its dismantling in 1839. Completed in 1787, the massive reflecting telescope used a metal mirror four feet in diameter and weighing over a ton. A wonder of the age, it quickly became a landmark visited by the rich and famous. By the time Sir John Herschel took this photograph, the telescope structure had become unsafe through neglect. This particular print is one of twenty-five made in 1890 from the original negative. It is mounted in a frame made from the ladder rungs of John Herschel's 20-foot telescope that he used at Slough and later near Cape Town, South Africa.