Читать книгу Electricity for Boys - James Slough Zerbe - Страница 5

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There is no study so profound as electricity. It is a marvel to the scientist as well as to the novice. It is simple in its manifestations, but most complex in its organization and in its ramifications. It has been shown that light, heat, magnetism and electricity are the same, but that they differ merely in their modes of motion.

First Historical Account.—The first historical account of electricity dates back to 600 years BC Thales of Miletus was the first to describe the properties of amber, which, when rubbed, attracted and repelled light bodies. The ancients also described what was probably tourmaline, a mineral which has the same qualities. The torpedo, a fish which has the power of emitting electric impulses, was known in very early times.

From that period down to about the year 1600 no accounts of any historical value have been given. Dr. Gilbert, of England, made a number of researches at that time, principally with amber and other materials, and Boyle, in 1650, made numerous experiments with frictional electricity.

Sir Isaac Newton also took up the subject atp. 6 about the same period. In 1705 Hawksbee made numerous experiments; also Gray, in 1720, and a Welshman, Dufay, at about the same time. The Germans, from 1740 to 1780, made many experiments. In 1740, at Leyden, was discovered the jar which bears that name. Before that time, all experiments began and ended with frictional electricity.

The first attempt to "bottle" electricity was attempted by Muschenbrœck, at Leyden, who conceived the idea that electricity in materials might be retained by surrounding them with bodies which did not conduct the current. He electrified some water in a jar, and communication having been established between the water and the prime conductor, his assistant, who was holding the bottle, on trying to disengage the communicating wire, received a sudden shock.

In 1747 Sir William Watson fired gunpowder by an electric spark, and, later on, a party from the Royal Society, in conjunction with Watson, conducted a series of experiments to determine the velocity of the electric fluid, as it was then termed.

Benjamin Franklin, in 1750, showed that lightning was electricity, and later on made his interesting experiments with the kite and the key.

Discovering Galvanic Electricity.—The great discovery of Galvani, in 1790, led to the recognitionp. 7 of a new element in electricity, called galvanic or voltaic (named after the experimenter, Volta), and now known to be identical with frictional electricity. In 1805 Poisson was the first to analyze electricity; and when Œrsted of Copenhagen, in 1820, discovered the magnetic action of electricity, it offered a great stimulus to the science, and paved the way for investigation in a new direction. Ampere was the first to develop the idea that a motor or a dynamo could be made operative by means of the electro-magnetic current; and Faraday, about 1830, discovered electro-magnetic rotation.

Electro-magnetic Force.—From this time on the knowledge of electricity grew with amazing rapidity. Ohm's definition of electro-motive force, current strength and resistance eventuated into Ohm's law. Thomson greatly simplified the galvanometer, and Wheatstone invented the rheostat, a means of measuring resistance, about 1850. Then primary batteries were brought forward by Daniels, Grove, Bunsen and Thomson, and electrolysis by Faraday. Then came the instruments of precision—the electrometer, the resistance bridge, the ammeter, the voltmeter—all of the utmost value in the science.

Measuring Instruments.—The perfection of measuring instruments did more to advance electricityp. 8 than almost any other field of endeavor; so that after 1875 the inventors took up the subject, and by their energy developed and put into practical operation a most wonderful array of mechanism, which has become valuable in the service of man in almost every field of human activity.

Rapidity of Modern Progress.—This brief history is given merely to show what wonders have been accomplished in a few years. The art is really less than fifty years old, and yet so rapidly has it gone forward that it is not at all surprising to hear the remark, that the end of the wonders has been reached. Less than twenty-five years ago a high official of the United States Patent Office stated that it was probable the end of electrical research had been reached. The most wonderful developments have been made since that time; and now, as in the past, one discovery is but the prelude to another still more remarkable. We are beginning to learn that we are only on the threshold of that storehouse in which nature has locked her secrets, and that there is no limit to human ingenuity.

How to Acquire the Vast Knowledge.—As the boy, with his limited vision, surveys this vast accumulation of tools, instruments and machinery, and sees what has been and is now beingp. 9 accomplished, it is not to be wondered at that he should enter the field with timidity. In his mind the great question is, how to acquire the knowledge. There is so much to learn. How can it be accomplished?

The answer to this is, that the student of to-day has the advantage of the knowledge of all who have gone before; and now the pertinent thing is to acquire that knowledge.

The Means Employed.—This brings us definitely down to an examination of the means that we shall employ to instil this knowledge, so that it may become a permanent asset to the student's store of information.

The most significant thing in the history of electrical development is the knowledge that of all the great scientists not one of them ever added any knowledge to the science on purely speculative reasoning. All of them were experimenters. They practically applied and developed their theories in the laboratory or the workshop. The natural inference is, therefore, that the boy who starts out to acquire a knowledge of electricity, must not only theorize, but that he shall, primarily, conduct the experiments, and thereby acquire the information in a practical way, one example of which will make a more lasting impression than pages of dry text

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Throughout these pages, therefore, I shall, as briefly as possible, point out the theories involved, as a foundation for the work, and then illustrate the structural types or samples; and the work is so arranged that what is done to-day is merely a prelude or stepping-stone to the next phase of the art. In reality, we shall travel, to a considerable extent, the course which the great investigators followed when they were groping for the facts and discovering the great manifestations in nature.

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