Michael Faraday and an electric shock machine.
ELECTRIC LIGHT
By Anon
Chatterbox Annual (1908)
I apologise for the quality of the illustrations. The book was in a very bad condition and this was the best I could do.
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Michael Faraday and an electric shock machine. |
Every boy has played with magnets, and watched with delight how they pick up needles, pens, keys, and other objects of steel and iron. Scientists, too, have played with magnets, but they have given much study to their play, and the result has been many wonderful and useful inventions.
It is now nearly eighty years since Professor Faraday, a distinguished chemist, showed that there was much similarity between magnetism and electrcity, and that the one could be made to produce the other. Among many other discoveries, he found that when a piece of iron is brought near to the ends or poles of a magnet, there is a little wave, as it were, of electricity passing through the iron for a moment just as it touches the magnet. In the smae way there is another momentary wave of electricity in the iron when it is pulled away from the poles of the magnet.
Other experimenters soon saw that if they could only make the iron move very quickly to and from the magnet, they might make the waves of electricy follow each other so rapidly as to create an electric current. They tried various ways of doing this, and by-and-by success rewarded their efforts. The simplest means of creating the current was to fix two pieces of iron to a rod, one at each end, and make it spin round, like two spokes of a wheel, near the poles of the magnet. As each piece of iron whirled round in its circular path, it passed rapidly across the poles of the magnet, and every time it did so waves of electricty were sent through it. Each piece of iron had a long wire wrapped round it in many coils, which gathered up the waves of electricity, and delivered them as a current at a suitable part of the machine.
Nearly everyone has held the handles of a magneto-electric machine at some time or other, and received an electric shock or current. The machine which produces it is usually such a one as I have described. Electric currents are sometimes beneficial to persons who are suffering from certain diseases, and chemists sell little machines for producing the currents. These machines are packed in small, narrow boxes, and on opening the lid we have no difficulty in discovering the horse-shoe magnet, and the little irons wrapped with silk-covered wires, which look like bobbins. The latter are turned by means of a wheel and handles, and there are smooth metal handles for the patient to grasp when he wishes to receive an electric shock.
These are among the smallest magneto-electric machines which are made. Large machines of a very similar kind are used for generating the electricity for electric light, electric trams, and many other purposes. These are usually known as dynamos, and a steam-engine is, as a rule, required to put them in motion. They vary a great deal in shape, but the chief fact to be remembered is the simple one that the electricity which they produce is obtained by whirling iron wire-covered bobbins close to the poles of one or more large magnets.
When we take hold of the handles of an electric machine, we feel a peculiar throb and shaking, which is caused by the passing of a current, as we call it, from one handle to the other. We feel nothing so long as we only touch one handle, but the moment we take hold of both, and make our body a sort of bridge between them, we feel the effects of the current.
We might make a bridge of various materials for the current, and we should sometimes obtain some curious results. If we used a thin platinum wire, we should find that the current made it warm, because of its resistance to the amount of current going through. Indeed. if the wire were very thin, it would become red-hot or incandescent, and we should have a glowing light produced by electricity; loops of fine platinum wire are largely used by doctors. The great chemist, Sir Humphry Davy, tried a bridge made of sticks of charcoal, and he found that they burned with an exceedingly brilliant light, more dazzling than any other artificial light which he had seen. This experiment was made long before Faraday made his experiments with magnets, and Sir Humphrey Davy obtained his electricity from an electric battery made up of about two hundred vessels containing chemicals and metal plates joined to each other by wires. He attached a stick of charcoal to each of the end wires of his battery, and when he brought the sticks together he obtained the brilliant light.
The large electric lights, enclosed in great globes, which we now employ in our streets and stations - the arc lamps as they are called - are only an improved form of Sir Humphrey Davy's electric light. It was found that the sticks of charcoal burned away very quickly, and rods of hard and specially prepared coke or carbon are now used in place of them. They wear away a little when the current is passing through them, and the lamps are provided with clockwork or electrical mechanism, which moves the carbons towards each other as they are consumed.
The small pear-shaped electric lights - the incandescent lamps which are used in houses and shops - are somewhat different from the arc lamps. The tiny globes enclose a slender thread which has been half burnt or charred by a special process. The current of electricity passes through this thread in its course from one wire to the other, and it makes the thread incandescent, so that it gives off a glowing light. In order to prevent the charred thread burning away, the air is taken out of the globe when the thread is inserted. As this kind of lamp requires no air and gives out little or no heat, it may be used in places where it would be impossible to light an ordinary lamp. The diver, for instance, is able to take an electric lamp with him to the bottom of the sea.
The dynamo in the illustration is of a common type. It can be made to generate electricity by being driven by a leather belt attached to some motive power, such as a gas engine. The belt is attached to the driving-wheel at the right end.