In 1785 Herschel approached King George for money to cover the cost of building the 40-foot telescope. He received £4,000. Without royal patronage, the telescope could not have been created. As it was, it took five years, and went over budget. The Herschel home in Slough became a scramble of "labourers and workmen, smiths and carpenters". A 40-foot telescope tube had to be cast of iron. The tube was large enough to walk through. Mirror blanks were poured from Speculum metal, a mix of copper and tin. They were almost in diameter and weighed . When the first disk deformed due to its weight, a second thicker one was made with a higher content of copper. The mirrors had to be hand-polished, a painstaking process. A mirror was repeatedly put into the telescope and removed again to ensure that it was properly formed. When a mirror deformed or tarnished, it had to be removed, repolished and replaced in the apparatus. A huge rotating platform was built to support the telescope, enabling it to be repositioned by assistants as a sweep progressed. A platform near the top of the tube enabled the viewer to look down into the tube and view the resulting image. In 1789, shortly after this instrument was operational, Herschel discovered a new moon of Saturn: Mimas, only in diameter. Discovery of a second moon (Enceladus) followed, within the first month of observation. The telescope proved very cumbersome, and in spite of its size, not very effective at showing clearer images. Herschel's technological innovations had taken him to the limits of what was possible with the technology of his day. The 40-foot would not be improved upon until the Victorians developed techniques for the precision engineering of large, high-quality mirrors. William Herschel was disappointed with it. Most of Herschel's observations were done with a smaller , reflector. Nonetheless, the 40-foot caught the public imagination. It inspired scientists and writers including Erasmus Darwin and William Blake, and impressed foreign tourists and French dignitaries. King George was pleased. Herschel discovered that unfilled telescope apertures can be used to obtain high angular resolution, something which became the essential basis for interferometric imaging in astronomy (in particular aperture masking interferometry and hypertelescopes). Reconstruction of the 20-foot telescope In 2012, the BBC television programme Stargazing Live built a replica of the 20-foot telescope using Herschel's original plans but modern materials. It is to