Fig. 110. Train unlocked and running.
Note position of L and M.
The relative position of the locking lever L and the rack hook is also very clearly shown in [Fig. 108]; that is, when the rack hook is pressed clear home at the lower notch of the rack, the lever L should safely lock the train and the lever M be resting with its link against the center arbor.
CHAPTER XIX.
THE CONSTRUCTION OF SIMPLE
AND PERPETUAL CALENDARS.
In taking up the study of calendar work the first thing that the student observes is the irregularity of motion of the various members. Every other portion of a clock has for its main object the attainment of the nicest regularity of motion, while the calendar must necessarily have irregular motion. The hand of the day of the month proceeds around its dial regularly from 1 to 28 and then jumps to 1 in February of some years, while it continues to 29 in others; sometimes it revolves regularly from 1 to 31 for several revolutions and then jumps from 30 to 1. What is the reason of this?
If the moon’s phases are shown they do not agree with the changes of the month wheels, but keep gaining on them, while if an “equation of time” is shown, we have a hand that moves irregularly back and forth from the Figure XII at the center of its dial. What is the cause of this gaining and losing?
In order to understand this mechanism properly we shall have to first know what it is intended to show and this brings us to the study of the various kinds of calendar.