Calendar of Discovery and Invention


August 28 —The most magnificent eighteenth - century telescopes, the great forty - foot reflector built by Herschel at Slough, was begun in 1785 and finished in 1789. It was built at the expense of George III. HJerschal gave a description of it in the Philosophical Transactions in 1795. The first was placed in the tube in February 1787 but was unsatisfactory; tho second was cast in January 1788 out cracked, while the third and last was cast a month later. On Oct. 24 of that year Saturn was observed with it, “but,” said Herschel, “not being satisfied, I continued to work upon it till Aug. 27, 1789, when it was tried upon the fixed stars and 1 found it to give a pretty sharp image.” Then he continues, “Aug. 28, 1789, Having brought the telescope to the parallel of Saturn, I discovered a sixth satellite of that planet; and also saw. the spots upon Saturn better than I had ever seen them before; so that I may elate the finishing of the 40-feet tele scope from that time.”

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S., E. Calendar of Discovery and Invention. Nature 120, 318 (1927).

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