from The Century Dictionary and Cyclopedia
- n. A form of clock which drives a mechanism or apparatus, as a telescope, heliostat, or chronograph, at a uniform rate which is directly related to the passage of time.
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The driving-clock and worm-gear that cause the 100-inch Hooker telescope to follow the stars
These bearings must be aligned exactly parallel to the axis of the earth, and must support the polar axis so freely that it can be rotated with perfect precision by the driving-clock, which turns a worm-wheel 17 feet in diameter, clamped to the lower end of the axis.
Within the pier are a photographic dark room, a room for silvering the large mirror (which can be lowered into the pier), and the clock-room, where stands the powerful driving-clock, with which the telescope is caused to follow the apparent motion of the stars.
The parts of the telescope which are moved by the driving-clock weigh about 100 tons, and it was necessary to provide means of reducing the great friction on the bearings of the polar axis.
Almost the entire weight of the instrument is thus floated in mercury, and in this way the friction is so greatly reduced that the driving-clock moves the instrument with perfect ease and smoothness.
As this motion must be sufficiently uniform to counteract exactly the rotation of the earth on its axis, and thus to maintain the star images accurately in position in the field of view, the greatest care had to be taken in the construction of the driving-clock and in the spacing and cutting of the teeth in the large worm-wheel.
The driving-clock and worm-gear that cause the 100-inch Hooker telescope to follow the stars.]