Both clocks and watches are “machines” for the measurement of time, and, therefore, it is absolutely imperative that their action must be constant, and, if accurate time is to be indicated, the action must be uniform. [Illustration: INTERIOR OF ASTRONOMICAL OBSERVATORY, SHOWING TRANSIT INSTRUMENT. USED TO OBTAIN CORRECT LOCAL TIME, BY OBSERVING THE PASSAGE OF STARS ACROSS THE MERIDIAN] [Illustration: BALANCE COCK AND PATENT MICROMETRIC REGULATOR; ALSO BALANCE WHEEL AND HAIR SPRING, SHOWING PATENT HAIR SPRING STUD] The illustration shows the “time train” of an ordinary pocket watch. The various wheels are here shown in a straight line, so that their successive order may be seen, but for economy and convenience they are arranged in such way as is most convenient when constructing a pocket watch. The large wheel at the left is the “main wheel,” called by watchmakers the “barrel.” In it is coiled the mainspring--a strip of steel about twenty-three inches long, which is carefully tempered to insure elasticity and “pull.” The outer end of the mainspring is attached to the rim of the barrel, and the inner end to the barrel arbor. Bear in mind the fact that the power which is sufficient to run the watch for thirty-six hours or more, is not in the watch itself. It is in yourself, and by the exertion of your thumb and finger, in the act of winding, you transfer that power to the spring, and thereby store the power in the barrel, to be given out at the rate which the governing mechanism of the watch will permit. The group of wheels here shown are known as the “time train,” and the second wheel is called the “center,” because that, in ordinarily constructed watches, is located in the center of the group, and upon its axis are put the “hour hand” and the “minute hand.” On the circumference of the barrel are gear teeth, and those teeth engage corresponding teeth on the arbor of the center. These arbor teeth are in all cases called, not “wheels” but “pinions,” and in watch trains the wheels always drive the pinions. Next to the center comes the third pinion and wheel, and then the fourth, which is the last wheel in the train which has regular gear teeth. Now let us look back a little and see that the wheel teeth of the barrel drive the center pinion, and the center wheel drives the third pinion and the third wheel drives the fourth pinion, etc. The speed of revolution of the successive wheels increases rapidly. The center wheel must revolve once in each hour, which is 6-1/2 times faster than the barrel. The third wheel turns eight times faster than the center, and the fourth wheel turns 7-1/2 times faster than the third, or 60 times faster than the center, so that the fourth pinion, which carries the “second hand,” will revolve 60 times while the “center,” which carries the minute hand, revolves once. If we should put all the wheels and pinions in place, and wind up the main spring, the wheels would begin to turn, each at its relative rate