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of William Herschel.
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against the next winter. The carpenters and smiths of Datchet were in daily requisition, and, as soon as patterns for tools and mirrors were ready, my brother went to town to have them cast, and, during the three or four months Alexander could be absent from Bath, the mirrors and optical parts were nearly completed.
"But that the nights after a day of toil were not given to rest, may be seen by the observations on Mars, of which a paper, dated December 1, 1783, was given to the Royal Society. Some trouble, also, was often thrown away, during those nights, in the attempt to teach me to remeasure double stars with the same micrometers with which former measures had been taken, and the small twenty-foot was given me for that purpose.... I had also to ascertain their places by a transit instrument lent for that purpose by Mr. Dalrymple; but, after many fruitless attempts, it was seen that the instrument was, perhaps, as much in fault as my observations."In 1783 Herschel says:
"I have now finished my third review of the heavens. The first was made with a Newtonian telescope something less than seven feet focal length, a power of 222, and an aperture of four and a half inches. It extended only to stars of the first, second, third, and fourth magnitudes. My second review was made with an instrument much superior to the other, of 85.2 inches focus, 6.2 inches aperture, and power 227. It extended to all the
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