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116 the Yerkes Observatory. It was designed originally by Sir Howard Grubb, for use with the great Lick telescope; and has been generally adopted for all large telescopes of that pattern. Presently we will notice a different method of working a large telescope,

but before doing so I want to remind you that since our Earth is steadily turning round on its axis, a telescope would soon lose a star unless there is clockwork to counteract the Earth's motion. You know how the various constellations change during the year: there is a little rhyme, made by the good Dr. Watts, which enables us to remember some of them, perhaps you know it already—