Centrifugal Force.
Closely connected with the spiral principle is Centrifugal Force, that marvellous power which gives to our whole solar system its ceaseless movements, and may extend, as far as we know, to other and vaster systems yet unknown.
Tie a ball to a string, and swing it round, and it will be an exact, though rough, representation of the double power by which the movements of the heavenly bodies are governed, our earth being included among them.
The string represents the force of attraction, which binds all our planets to the sun, and their satellites to the planets, while the force that is employed in swinging the ball represents the mysterious power that issues from the sun, and gives motion to the planets. The metaphor is a very homely one, but it is nevertheless correct.
In the accompanying illustration are several examples of Centrifugal Force as found both in Nature and Art. On the left hand we have diagrams of some of the heavenly bodies, showing the revolution of their offspring, so to call them, while on the right are seen examples of Centrifugal Force as applied to human use. For convenience’ sake, the illustrations have been separated into two portions.
In the first of these illustrations we have the “Governor” of the steam-engine, that wonderfully ingenious and simple piece of mechanism which controls the force of the steam, and, without the superintendence of man, acts almost as a living being might.
It is composed of two heavy metal balls, hinged, as shown in the illustration, to a movable collar which slides up and down the central rod. When the engine is at work the Governor revolves, and the harder it works, the more rapid is the revolution. Consequently, as it revolves, the balls diverge and draw the sliding collar up the rod.
Here lies the whole beauty of the invention. The sliding collar is connected with the safety-valve. Thus, if the engine should be working beyond its proper powers, the Governor draws up the collar, and releases sufficient steam to take the undue pressure off the boiler. Thus the engine may be left, so to speak, to manage itself.
Next are shown two examples of Centrifugal Force as applied in ancient warfare, namely, the Sling, which is now retained merely as a boy’s toy, and the Amentum, which was practically a sling attached to a spear. Both weapons have been superseded by the modern firearms, but the Sling is really a more formidable offensive weapon, in skilful hands, than is generally suspected.
A good slinger is as sure of his aim as a good rifleman, and can send his missile to a wonderful distance. Were I to be armed with the best pistol hitherto invented, I should be sorry to fight an accomplished slinger, unless under cover.
The really tremendous power of the Sling is obtained by Centrifugal Force, the weapon, with its missile, being whirled in the air, and then one string being loosed with a peculiar knack something like the “loose” of a good archer. In consequence, the centrifugal force is converted into direct force, and the missile flies directly forwards.
The Amentum is simply a cord tied to a javelin, so that the thrower has the advantage of a lever, which, after all, is only the conversion of centrifugal force.
The very familiar Mop, flinging off its moisture to a considerable distance, needs no description; but I have introduced it to show the action of centrifugal force in small as well as in great things.
The next illustration shows how this very same power acts upon the greatest as well as the least of objects, and enables them to maintain positions which otherwise they must of necessity fail to do. Take, for example, our own Earth, and its peculiar position of being tilted on one side, so as to give us the alternative seasons as it flies on its annual course.
This is simply due to its own rapid revolution, which, on the same principle that keeps the arrow and the rifle-ball straight on their course, prevents it from altering its position.
The very same principle acts on the boys’ Tops, and is shown in a really remarkable manner by the professional Japanese top-spinners, who will place several tops upon each other, as shown in the illustration, and make them sway backwards and forwards in the most extraordinary manner, sometimes being all upright, and sometimes leaning almost at right angles to each other.
A favourite mode of illustrating this power of Centrifugal Force is by the Gyroscope, a figure of which is given on the right hand of the illustration. The interior wheel is made to revolve rapidly, and the effect of the revolution is to enable the instrument to maintain a horizontal position, even when suspended on one side, as shown in the engraving.
The power of this revolution is quite wonderful, even in a small Gyroscope which can be purchased for a few shillings. It almost seems to be alive, and to insist on retaining its position, in spite of all efforts to the contrary.
This principle is used in the swinging cabin of the Bessemer ship, and is also employed by quoit-players in keeping their missile steady as it flies towards the mark. Even the now fashionable Bicycle is managed on the same principle.
As is well known to all bicycle riders, it is comparatively easy to maintain the balance when the pace is rapid and the wheels revolving quickly. The difficulty is, to do so when the pace is slow, and the rider is deprived of the centrifugal force which keeps him on his balance almost in spite of himself. It is just the same with a child’s hoop, which runs straight and upright when it is driven rapidly, or when, for example, it runs downhill. But, as soon as the centrifugal force is expended, it begins to waver, loses its direction, and soon falls to the ground.
USEFUL ARTS.
CHAPTER XVII.
OSCILLATION.—UNITED STRENGTH.—THE DOME.
Connection of Oscillation with Centrifugal Force.—Equality of Time in Oscillation.—The Spider.—The Stone and String.—Pendulum of the Clock, and its Effect on the Machinery.—Acceleration and Retardation.—Compensating Pendulums.—The Metronome, and its Use in Music.—A simple Metronome.—Value of the Instrument in War.—The Escapement, and its Connection with the Pendulum.—Mode of Action.—Larva of Burying-beetle.—Earthworms and Serpents.—Union is Strength.—The Hippopotamus Rope and its Structure.—The Spider-web.—Distinction between the Threads.—Principle of the Dome.—The Arch, and its Connection with the Dome.—Esquimaux Huts.—Receiver of the Air-pump, and its Power of Resistance.—The Human Skull and the Egg.—Accidental Resemblance.—The Salad-dressing Bottle.—The Medusa, Strobila, and Hydra.
A portion of our last chapter dealt of Centrifugal Force. We will now proceed to another well-known power, which seems to be a variation, or perhaps a division, of the same power. I mean the principle of Oscillation, which has done so much for the present state of the world. I mention the connection of the two principles because it is evident that, if Oscillation were continued in one direction, it would be converted into centrifugal force. In fact, it can only be considered as centrifugal force interrupted.
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.
A very good Metronome may be made by fastening a bullet to the end of a piece of tape, and swinging it backwards and forwards, regulating the tape according to the time required. Such a Metronome is very portable, and extremely useful where the conveyance of the clockwork instrument would be troublesome. Moreover, its beats can be seen by a great number of persons. I have often used it myself.
Such a Metronome is used in the army, in order to regulate the pace of the soldier’s step, it being of the last importance that the pace should always be the same. Otherwise it would be impossible to calculate the time which ought to be consumed in marching a certain distance, and the military calculations on which depends the success or failure of a campaign would be wholly upset, half an hour too soon or too late meaning failure.