Читать книгу The Modern Clock. A Study of Time Keeping Mechanism; Its Construction, Regulation and Repair онлайн
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Further, a pointer is attached to the lower end of the pendulum, for reading off the arc of oscillation.
The essential advantages of this pendulum over the mercurial compensation pendulums are the following:
(1.) It follows the changes of temperature more rapidly, because a small amount of mercury is divided over a greater length of pendulum, whereas, in the older ones the entire (and decidedly larger) mass of mercury is situated in a vessel at the lower end of the pendulum rod.
(2.) For this reason differences in the temperature of the air at different levels have no such disturbing influence on this pendulum as on the others.
(3.) This pendulum is not so strongly influenced as the others by changes in the atmospheric pressure, because the principal mass of the pendulum has the shape of a lens, and therefore cuts the air easily.
CHAPTER V.
REGULATIONS, SUSPENSIONS, CRUTCHES
AND MINOR POINTS.
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Regulation.—The reader will have noticed that in describing the various forms of seconds pendulums we have specified either eighteen or thirty-six threads to the inch; this is because a revolution of the nut with such a thread gives us a definite proportion of the length of the rod, so that it means an even number of seconds in twenty-four hours.