Clocks not lettered in the bottom of the case must be wound before starting the pendulum. To do this press the switch shown in [Fig. 136], which is on the left side of the case and under the dial.
Continue the pressure until the winding ceases. Then set the hands and start the pendulum in the usual way. If the bell is not wanted to ring, bend back the hammer.
Secondary Dials.—One of the most deceptive branches of clock work is the secondary dial, or “minute jumper.” Ten years ago it was the rule for all manufacturers of electric clocks to put out one or more patterns of secondary dials. Theoretically it was a perfect scheme, as the secondary dial needed no train, could be cheaply installed and could be operated without trouble from a master clock, so that all dials would show exactly the same time. Practically, however, it proved a very deceptive arrangement. The clocks were subject to two classes of error. One was that it was extremely difficult to make any mechanical arrangement in which the hands would not drive too far or slip backward when the mechanism was released to advance the minute hand. The second class of errors arose from faulty contacts at the master clock and variation in either quantity or strength of current. Another and probably the worst feature was that all such classes of apparatus record their own errors and thereby themselves provide the strongest evidence for condemnation of the system. Clocks could be wound once an hour with one-sixtieth of the chance of error of those wound once per minute, and they could be wound hourly and synchronized daily with ¹⁄₁₄₄₀th of the line troubles of a minute system.
The minute jumpers could not be synchronized without costing as much to build and install as an ordinary self-winding clock, with pendulum and time train, and after trying them for about ten years nearly all the companies have substituted self-winding time train clocks with a synchronizing system. They have apparently concluded that, since it seems too much to expect of time apparatus that it will work perfectly under all conditions, the next thing to do is to make the individual units run as close to time as is commercially practicable and then correct the errors of those units cheaply and quickly from a central point.
It is for these reasons that the secondary dial has practically disappeared from service, although it was at one time in extensive use by such companies as the Western Union Telegraph Company, the Postal Telegraph and the large buildings in which extensive clock systems have been installed.
[Fig. 143] shows one form of secondary dial which involves a screw and a worm gear on the center arbor, which, it will be seen, is adapted to be turned through one minute intervals without the center arbor ever being released from its mechanism. This worm gear was described in the American Jeweler about fifteen years ago, when patented by the Standard Electric Time Company in connection with their motor-driven tower clocks, and modifications of it have been used at various times by other companies.
The worm gear and screw system shown in [Fig. 143] has the further advantage that it is suitable for large dials, as the screw may be run in a box of oil for dials above four feet and for tower clocks and outside work. This will readily be seen to be an important advantage in the case of large hands when they are loaded with snow and ice, requiring more power to operate them.
Fig. 143. Minute jumper. A, armature; M, magnets; W, worm gear
on center arbor; B, oil box for worm; R, four toothed ratchet.