Friday, October 07, 2005

Men Who Found Electricity - Part Four

The Danish Professor Who Turned the Compass from the North

Now we must think for a moment of magnets. They had long been made. Soft iron could be magnetised by rubbing the loadstone upon it, but magnets like these soon lost their magnetism. Steel, after being magnetised by the loadstone, does not lose its magnetism. Once a magnet, always a magnet, with the hard steel. Now, many clever men had been wondering if there might not be some connection between magnetism and electricity, and Professor Oersted, a Danish scientist, living at Copenhagen, found, in 1820, that by passing an electric current from a Voltaic battery through a wire he could alter the position of the magnetic needle.

The magnetic needle is the little steel pointer of the compass which, when not interfered with, points to the north. Oersted found that, though the whole earth is one vast magnet, its power to attract the magnetic needle to the north is not great enough to prevent the point of the needle from being drawn aside by a strong electric current. Oersted showed that when the wire bearing the electric current is placed over the needle, the needle turns its head from the north to the east, but that if the wire be placed underneath the needle, the needle turns its head to the west.

What Oersted did sounds an interesting trick for a conjurer to do, but see what the effect of it was. The fact that an electric current turns the magnet is the beginning of the power which enables us to have telegraphs and telephones, and to do all the work of which the marvellous electric current is capable. Oersted had opened the door to the great field of discovery in what we call electro-magnetism. But the discovery did not remain there, or it would have been of no use to mankind.

Michael Faraday, The Blacksmith's Son Who Helped to Change the World

It remained for one of the finest English sons of science to carry the work to perfection. This was Michael Faraday, who was born in 1791, the son of a poor London blacksmith. After very little schooling he was aprenticed to a bookbinder, and after working hard all day he would study science at night. One day a gentleman, on entering the shop, found the boy at work binding an encyclopaedia, and studying hard at the article in it on electricity.

The gentleman was surprised to see a boy so interested in a subject of such difficulty, and questioned him. He found that Faraday, working late at night, had already been making experiments of his own, though he was too poor to possess anything but an old bottle for his battery. The visitor was so pleased that he gave him four tickets for the lectures which Sir Humphry Davy was then delivering at the Royal Institution. Faraday was as pleased as if anybody had given him a fortune. He went to the lectures. He made notes of what he heard, and then at the end of the lectures he went, in fear and trembling, to the great man and showed him his notes.

Davy was surprised to see what the poor boy had done. But he remembered how poor he himself had been as a boy, and how he had had to struggle to educate himself, and his heart warmed towards the humble apprentice. Faraday told him that he wanted to be a scientist, and Davy, after doing all that he could to test his faith, had the boy appointed as his own assistant.

He helped him in his education, he took him on the Continent and let him make numberless experiments, and in course of time, when Faraday had grown up and become famous for his work in science, he succeeded the great man who had been so good a friend to him.

Faraday's life was a long, beautiful story of good and wonderful achievements. He did more for scientific learning than any other man of his day. His lectures and writings were upon the most difficult subjects, yet he wrote and talked so simply that even children could understand him and find delight in his words. All that he did for science is too much for us to talk of here; but the thing which we have to note is one of his wonderful discoveries concerning electicity and magnetism. Oersted had found that the electric current will turn the magnetic needle. Faraday worked until he discovered that the magnet will electrify wire through which no current is passing! That clearly established the relationship between magnetism and electricity.

The result of this was of great importance. It meant that men no longer had to depend upon the small current of electricity which was chemically produced in jars or batteries. First of all we have a coil of wire which, when electrified and placed near a magnet, itself becomes a magnet, with a north pole and a south pole, the north pole of the wire being attracted by the south pole of the magnet, and the south pole of the wire being attracted by the north pole of the magnet; while the north pole of the magnet drives away the north pole of the electrified wire, and the south pole of the magnet drives away the south pole of the wire.

But we can make the north and south poles of the wire change places. If we send the current in by one end, then the front of the wire is the north pole; if we send the current in by the other end of the wire, then the back part of the wire becomes the north pole. The moment the current is turned of, or the connection is broken, as we say, the coil of wire ceases to be a magnet.

William Sturgess, in 1825, made an electro-magnet of the highest value. He found that if we take a piece of soft iron and wrap wire about it, it becomes a far more powerful magnet, when electrified, than the ordinary magnet itself, and of course it can be made a magnet or not a magnet as often as we turn the current on or off. That gives us a powerful magnet which, as we have seen, can electrify any other coil of wire brought near it.

Faraday, working on, found that the coil of wire, on coming near the magnet, passed through what he called lines of force - certain avenues through which the magnetic influence is travelling. Therefore the more often that the coil passed through these lines of force the more often would it feel the effects.

The next step, therefore, was to make a coil of wire which was attached at its ends to a revolving wheel. The coil, by turning round rapidly, received repeated impulses from the magnet. The current set up in this coil can be led away by wires into a receiver and stored, to eb sent over wires hundreds or thousands of miles long, to do all manner of work, as often as it is wanted.

The use of the electro-magnet eneables us to et force for driving engines, for telegraphing and telephoning, for lifting huge weights, and for all sorts of work. It is perfectly obedient, for the electric current which controls it can be turned on or off at any moment. The greatest part of the foundations of electric science had now been laid. All that remianed was to apply to practical purposes the knowledge which these first workers had given the world.

Long intervals passed before we could take advantage of all the theories. The electric telegraph dates from about 1837; the cables under the sea from 1852, electric bells from about 1855, the telephone and electric light from about 1878. It was possible by 1883 to produce electricity in sufficient quantities to sell it like gas to people who wished to use it. In the same year the first electric trolleys began to run, and electric railways appeared in 1892.

Wireless telegraphy was known in its first stages long ago, but it was not until 1899 that it could be used. One of the most brilliant electricians was Lord Kelvin, who died only in 1907. He used to be Mr. William Thompson, but Queen Victoria honoured him by making him Lord Kelvin. We shall read more about him on another page.

So, from the rubbing of amber to make it attract chaff and pieces of straw, men got to friction machines and excited stockings; from that to the Leyden jar, and so on to the Voltaic pile and cell and battery; then on to the electro-magnet and the great dynamos, which use up the knowledge of the men who discovered electro-magnetism, and produce electricity enough to do half the work of the world.

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