Page:Popular Science Monthly Volume 26.djvu/680

662 at night, with the alarm set to call her up to get the family's breakfast. She sets the clock on an uneven table, and in a short time it will stop, and the girl will not be alarmed in the morning, except on discovering that the clock has stopped, and that she has far overslept herself. Thus, to make a sure clock, the manufacturers must make a poor one. For the best running of a fine clock it has been found that about twenty-seven pounds is the most satisfactory weight for the bob.

If it were not for what may be designated as meteorological changes, the problem of the accurate measurement of time would be solved if we had a heavy pendulum driven uniformly over a small arc. But here are two "ifs." We will take the second of them first, as it is more easily disposed of. Postulating at the outset machinery in the train very nicely executed, and with jeweled bearings so that it will act uniformly, or with the least possible variation, we have before us the question of propelling it uniformly. That the best power for a clock is a weight, is beyond dispute. The invention of the coil-spring came near annihilating the race of good common clocks. "Grandfather's clock," with its wooden wheels and other crudities, is still the superior of the grandson's clock as a time-keeper, for "grandfather's clock" had the great advantage of a uniform power sufficient and just sufficient to propel the clock when it was properly cleaned and oiled. The grandson's clock has a coiled-spring as a motive-power, having, when it is tightly wound, not less than three times the amount of power required to drive the clock, and diminishing in amount, thereby altering the rate of the clock, with each successive hour. The grandson's clock will march on, oiled or unoiled (and therefore usually unoiled), until it comes to a premature end as complete as that of the "one-hoss shay." The "grandfather's clock," on the other hand, which declined to go unless its rations of oil were doled out to it once in a year or less by the peripatetic tinker, is good for another century, since its bearings have been saved from cutting themselves away from lack of oil. The kitchen-clock of to-day can only be made to keep respectable time by so regulating it that the gain it makes when tightly wound shall be offset by the loss as it runs down. Something is gained in spring-clocks by resorting to the fusee—a device which maintains the power of the spring as it unwinds by giving it a greater leverage. This device was much employed by the makers during the early days of spring-clocks; but it was found to be so difficult a matter to secure a chain or cord for the connection that was reliable that the plan has been almost, if not altogether, abandoned. About the only opportunity of seeing a fusee to-day is in an English watch. It has been abandoned by watch-makers in America and in Europe, outside of England, so that the modern watch has no chain, and is made to go uniformly by adjusting to "isochronism," as it is called, which will be explained later.