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Catechism of Familiar Things; Their History, and the Events Which Led to Their Discovery, A

<h2>CHAPTER XIX.</h2> <h3>Attraction, Tides, Gravity, Artesian Wells, Air, Aneroid Barometer, Ear-Trumpet, Stethoscope, Audiphone, Telephone, Phonograph, Microphone, Megaphone, Tasimeter, Bathometer, Anemometer, Chronometer.</h3> What is Attraction? By attraction is meant that property or quality in the particles of bodies which makes them tend toward each other. Are there several kinds of attraction? Yes. Attraction has received different names, according to the circumstances under which it acts: The force which keeps the particles of matter together to form bodies or masses, is called attraction of cohesion; that which makes bodies stick together only on their surfaces, is called adhesion; that which inclines different masses toward each other, as the earth and the heavenly bodies, is called gravitation; that which forces the particles of substances of different kinds to unite, is known under the name of chemical attraction; that which causes the needle of the compass to point constantly toward the poles of the earth, is magnetic attraction; that which is excited by friction in certain substances, is known as electrical attraction. How do you know that attraction exists through the whole universe? This great universal law was first discovered by Sir Isaac Newton. The sun and planets and other heavenly bodies are only guided in their path by gravitation. Do we experience this attraction upon our earth? Yes; because our earth is carried around the sun by it; and, further, the tides show it very clearly. What are the Tides? The ebbing and flowing of the sea, which regularly takes [202]place twice in twenty-four hours. The cause of the tides is the attraction of the sun, but chiefly of the moon, acting on the waters of the ocean. What is Gravity? Gravity is the attraction between the earth and the bodies on the earth, which makes what we call weight of bodies. What do you understand by specific weight or gravity? It means the weight of a body as compared with the weight of an equal bulk of some other body taken as a standard—commonly water. Why do we say that certain metals—as, for example, platina or gold—are heavier than others, say, lead or iron? Because the former have a greater specific gravity. But is not a pound of gold as heavy as a pound of lead? Yes; but a lump of gold will be heavier than a lump of lead of equal bulk. Can we explain by this what we call floating? A body will float in water if its gravity is less than that of water; for example, wood floats for this reason in water, and a balloon in the air. Why does a portion of the floating body sink below the surface of the water? Because the body in order to float must displace a portion of water equal in weight to the whole floating body. But why do iron steamers float—iron being heavier than water? Because the steamer is not a solid piece of iron, but is hollow, and so increased in bulk; for that reason the weight of the vessel and its contents is less than that of an equal bulk of water. How can you ascertain that air has weight? We can do it by the barometer and by very many experiences in daily life. If one end of a straw be dipped into a vessel of water and the other end be sucked, the liquid will [203]rise to the mouth. There we see the pressure of the outside air forces the liquid through the straw where the air was removed by sucking. Can you show the same by another instrument? Yes; the common water pump demonstrates the same as the straw. A tube is placed into the water, the air is sucked out from the tube by the movement of the pump, and the outside air presses the water through the tube. What are Artesian wells? Wells so named because they were made first at Artois, in France. They work on the principle that every liquid seeks its level. Of the rain which falls, a part soaks into the soil of mountains, until, coming to a layer of rocks or clay through which it cannot pass, it will collect and be stored up. If a hole be bored into this reservoir the water will rise in it. Do you know some other properties of air? It is the most necessary substance for our life; it is the vehicle of all odors and smells; it is the medium of all sounds, and brings to our ear and so to our mind an immense knowledge of the outside world; it is the cause of the beauty of the blue firmament or sky, of the aurora and twilight; it is the great nurse of the whole vegetable kingdom by clouds, rain, and dew. What is an Aneroid Barometer? It is a barometer in the construction of which no quicksilver or other liquid is used. It consists of a metal box, exhausted of air, the top of which is of thin metal, so elastic that it readily yields to alterations in the pressure of the atmosphere. When the pressure increases, the top is pressed inwards; when, on the contrary, it decreases, the elasticity of the lid, aided by a spring, tends to move it in the opposite direction. These motions are transmitted by delicate levers to an index which moves on a scale. This barometer has the advantage of being portable. [204] What is the Ear-trumpet? A trumpet-like instrument used to aid deaf persons in hearing. Its form is conical, and the larger end is of a bell shape; the small end is placed in the ear, and the person talks in the large end. It acts by concentrating the voice on the listener's ear. What is a Stethoscope? An instrument used by physicians for ascertaining the action of the lungs, judging by the sound of their motion whether they are healthy or not. Describe the Audiphone. It is a fan-shaped instrument to help deaf people, and is made of flexible carbonized rubber. Fine silk cords attached to the upper edge bend it over, and are fastened by a wedge in a handle. The top edge of this fan rests upon the upper teeth, and the sound waves strike its surface; the vibrations are thus conveyed by the teeth and the bones of the face to the acoustic nerve in the ear. Describe the Telephone. It is an instrument by which conversation may be carried on at a distance, and is composed of three parts—a thin disk of soft metal, a small coil or bobbin of silk-covered copper wire, and a small bar magnet about four inches long. The bobbin is placed on one pole of the magnet, so that the wire is as it were steeped in the magnetic space round the pole. The metal disk is placed face close to the pole and bobbin, so that when it vibrates in front of the pole a series of wave currents will be set up in the coil of wire on the bobbin. The whole is encased in wood, and a mouth-piece is provided for speaking against the disk. The coil of wire on the bobbin is of course connected by its two ends into the circuit of a telegraph line. Who invented the Telephone? It was invented, almost simultaneously, by Alex. Graham [205]Bell, a native of Scotland, and Professor of Vocal Physiology in the Boston University, and Elisha Gray, of Chicago. What is a Phonograph? It is an instrument for recording the vibrations of sounds, and consists of a revolving cylinder covered with tin-foil. To this cylinder is attached a mouth-piece, fitted with a thin plate or disk, on the outer side of which, next to the cylinder, is a needle or point. The cylinder runs on a screw, so that the whole length of it, from end to end, may pass under the point. On speaking into the mouth-piece the voice causes the disk to vibrate, and the point to trace marks corresponding to these vibrations on the tin-foil. By turning the cylinder so that the point again passes into the marks in the tin-foil, the sounds that entered at the mouth-piece can be reproduced at any time. By whom was the phonograph invented? By Thomas A. Edison, who was born in Ohio in 1847. Mr. Edison is the inventor of many improvements in telegraphy, which have been adopted into general use, and are to him the source of a large income. To him, also, we are indebted for the megaphone, microphone, tasimeter, an improvement in the telephone, a system of electric lighting, and many other inventions. What is a Microphone? This instrument is a variety of telephone by means of which faint sounds can be heard at a very great distance. It consists of a small battery for generating a weak current of electricity, a telephone for the receiving instrument, and a speaking or transmitting instrument. The last is a small rod of gas carbon with the ends set loosely in blocks of the same material. The blocks are attached to an upright support, glued into a wooden base board. This instrument is connected with the battery and the telephone. So wonderfully sensitive is it, that the ticking of a watch, the walking of a [206]fly across a board, or the brush of a camel's-hair pencil can be heard even though it be hundreds of miles distant. Will you describe the Megaphone? It is a substitute for the ear and speaking trumpet. It consists of three paper funnels placed side by side. The two larger ones are about 6 feet 8 inches long and 27-1/2 inches in diameter, and are each provided with a flexible tube, the ends of which are held to the ear. The centre funnel, which is used as a speaking-trumpet, does not differ materially from an ordinary trumpet, except that it is larger and has a larger bell mouth. Two persons, each provided with a megaphone, can, without other apparatus, carry on a conversation at a distance of one and a half or two miles. What is the Tasimeter? It is an instrument, sensitive to the smallest degree of heat, and is mostly used in astronomy. Attached to a telescope it will show the heat coming from the stars. What is a Bathometer? This ingenious instrument, the invention of Prof. Siemens of London, enables those on board of ships to read from an index the depths of the ocean beneath them. It consists of a highly sensitive steel spring to which a heavy piece of metal is attached. The changes in weight to which the latter is subject in consequence of the variations of attractive force (the deeper the ocean the smaller the latter, and vice versa) are registered on a scale by the indicator that is in connection with the steel spring. What is an Anemometer? An instrument for measuring the velocity and force of the wind, and by which storms, at a distance, can be predicted. What is a Chronometer? A time-piece of delicate and exact construction, chiefly employed by astronomers and navigators. It differs only from an ordinary watch in its delicate springs, in not being so much [207]influenced by heat and cold, and consequently in its accuracy in giving the time. <hr style="width: 65%;" /> <div style="break-after:column;"></div>

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