1784. This review included all the stars of Flamsteed's catalogue and the small stars near them. The work was carried through with amazing rapidity. He would observe for ten or twelve hours at a stretch, and as many as 400 stars were observed and measured in the course of a night. Later in the same year, his attention was drawn to star-clusters and nebulae by the appearance of Messier's famous catalogue, and accordingly on 28th October, 1783, he began to "sweep the heavens" for these objects with his new 20-foot reflector of 18.7 inches aperture, and at the same time to "gauge" the depth of the sidereal system. A number of experimental observations were made, and on 18th December he commenced his systematic "sweeps," which were continued till 1802.
In this work he found his sister an invaluable helper. In 1782, she tells us, her thoughts were "anything but cheerful". "I found I was to be trained as an assistant-astronomer, and by way of encouragement, a telescope adapted for 'sweeping,' consisting of a tube with two glasses, such as are commonly used in a 'finder' was given me. I was to 'sweep for comets'. . . . But it was not until the last two months of the same year that I felt the least encouragement to spend the star-light nights on a grass-plot covered with dew or hoar-frost without a human being near enough to be within call. . . . All these troubles were removed when I knew my brother to be at no great distance making observations with his various instruments, on double stars, planets, etc., and I could have his assistance immediately when I found a nebula, or cluster of stars, of which I intended to give a catalogue; but at the end of 1783 I had only marked fourteen, when my sweeping was interrupted by being employed to write down my brother's observations with the large 20-foot." Caroline's observations are preserved in three volumes of quarto and four of folio. These observations were at first not unattended by danger. They
