The chief point in this subject is the equal time occupied by the oscillating body, no matter what may be the “arc” distance through which it sways, provided that the length of the line remains the same. The discovery of this principle by Galileo in a church at Florence is too well known to need repetition.
This principle may be observed by any one, and at almost any time. The Spider at the end of its line illustrates it, and so does a stone tied to a string, both of which objects are shown in the illustration.
In various departments of Art, Oscillation is absolutely invaluable. We will take, for instance, the best known of these examples, namely, the Pendulum, by which the movements of clocks are regulated. Without some mode of regulation, the works would run down rapidly, and the clock rendered incapable of measuring time. But, in the Pendulum, we possess a means of making a clock go at any desirable rate, and be faster and slower at pleasure; a long Pendulum working slowly, and a short one rapidly.
How the Pendulum affects the working of a clock may be seen by reference to the right-hand figure of the illustration. The movements of the clock are connected with the Pendulum by means of an ingenious piece of mechanism called an “escapement,” because it only allows the wheel shown in the illustration to move one cog at each swing of the Pendulum.
Now, as in the latitude of London a pendulum which is a trifle more than thirty-nine inches in length swings once in a second, it is evident that, by lengthening or shortening the Pendulum, we have the rate of the clock entirely under command.
For example, if a Pendulum be required to swing once in two seconds, it must be four times as long as that which swings once in one second, while to swing once in three seconds it must be nine times as long, the length being measured by the square of the time of vibration.
We are thus able to “regulate” clocks by lengthening the Pendulum if they be too fast, and shortening them if they be too slow. The reader will probably have remarked that the conditions of the atmosphere—such as heat, cold, moisture, or dryness—must have an effect on the length of the Pendulum, and thus alter the rating of the clock. So they do, and in consequence the Compensating Pendulums have been invented, some of them being made of metallic rods of different powers of expansion, mostly brass and steel, while others carry a quantity of mercury in a glass tube near the bottom of the Pendulum.
Another familiar example of the Pendulum is the Metronome, which is simply a Pendulum with a weight at the top as well as counterpoise below the bottom, the weight moving up or down so as to decrease or hasten the pace. Generally a bell is added to it, which is struck at the beginning of each bar.
The exactness of its beats is perfect, as is known to all musicians, and is calculated to take the conceit out of players who are apt to disregard their time. I knew one lady, a really good pianiste, before whom I placed my Metronome. Before she had played many bars she broke down, exclaiming that the horrid bell always said “ting” in the wrong place. However, she soon acknowledged the value of the instrument, and was glad to use it.