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16 was stimulated by "Astronomy Explained upon Sir Isaac Newton's Principles," by James Ferguson, the Scottish astronomer. Herschel's early interest in the latter science seems to have been revived. So enthusiastic did he become that, in his own words, "I resolved to take nothing upon trust, but to see with my own eyes all that other men had seen before". At the time of his sister's arrival at Bath, Herschel had plunged in earnest into the study of astronomy. "He went to sleep," she tells us, "buried under his favourite authors; and his first thoughts on rising were how to obtain instruments for viewing these objects himself of which he had been reading." In May, 1773, he procured some object-glasses which he fitted into pasteboard tables. Caroline Herschel, who at that time had no interest whatever in telescopic astronomy, tells us: "I was much hindered in my musical practice by my help being continually wanted in the execution of the various contrivances, and I had to amuse myself with making the tube of pasteboard for the glasses which were to arrive from London". At length, Herschel completed this instrument, 4 feet long, which magnified forty times. With this, he records, he observed Jupiter and its satellites. Afterwards he made other two refractors—15 and 30 feet long respectively. Herschel soon discovered for himself the great weakness of the refracting telescope—the long tubes which were then necessary in order to counteract the effect of chromatic aberration. Finding the long tubes almost "impossible to manage," he turned his attention to the reflecting telescope, and in September hired a two-foot Gregorian reflector, which he found much more convenient. He decided to acquire a mirror of his own, for a tube 5 or 6 feet long. On enquiry he found there were none in the market of so large a size. "A person," his sister tells us, "offered to make one at a price much above what my brother thought proper to give." Herschel, however, was not discouraged. He