The Library of Work and Play: Electricity and Its Everyday Uses

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o the club, the programme committee determined the time and order of presentation. I found that I had been made an honorary member of this committee and that it was expected that I should steer the committee. I told them that I accepted this appointment with the understanding that the fellow who steers is always the smallest man in the crew, and if they would do all the

ammeter. I told the committee to make that the subject of the next meeting and to send to m

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enerally in pairs. When the boys came they fo

oys exclaimed that from my reference to the watch he had expected to see very complicated machinery with many wheels, but from the exceeding simplicity of the mechanism he could not see why it should cost sixty dollars. I told him that although it was a fine piece of

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arrangement a mag

at will repel a portion of your compass needle as well as other portions in both horseshoe and needles which attract each other." Whereupon, they found that the portion marked N (Fig. 13) repelled the blue end of the compas

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eel magnets gradually lose their strength. How th

as we did that of another magnet upon a former occasion, you will find that although this is a strong steel magnet i

e? The spool-like thing between the poles of the magne

little magnet with poles. I will send an electric current through the wire which surrounds this armature, and you notice that the needle which it carries moves to the right. Notice that the lower end of this armature acts like the blue end of your compass needle in that it is repelled from the pole N of the field and is attr

l now send the current through a 32-candle-power lamp, and you notice that the needle points to one, indicating that one ampere is required to light that lamp. But what prevents the needle from going farther, and what brings it back to zero each time?" The boys discovered a very small spring, like the hair spring of

n 1775, the year our Revolutionary War broke out. He died in 1836. When Oersted made his famous discovery of the action of an electric current upon a magnetic needle, in 1819, Am

inasmuch as the zero is in the middle of the scale we may with this instrument both measure the amount of current and tell its direction. You will recall that when we connected the magneto with this instrument, it indicated that the magneto sent the current first in one direction and then in the other, which we call an 'alternating current.' But you notice that the current which I am using in this laboratory flows continuously in one direction. This is called the 'direct current.' We shall find out how a dynamo may produce a direct current at another time. Let us not forget, however, that we have repeated Ampère's discovery, and found out that

djust the cocks so that one tenth of the water would go through a and nine tenths through s. Or, indeed, without stop-cocks, the size and length of s and a might be so apportioned that one tenth of the water would flow through a and nine tenths through s. This is precisely the adjustment which has been made with reference to the flow of electricity through this instrument. s is called a 'shunt.' When the shunt i

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urnish two amperes as one, and twice as much coal must be consumed to furnish an ampere for two hours as for one hour. Hence

meant that the field and armature were wound parallel to one another, as shown by diagram in Fig. 15. In which case the electric current which the machine generates divides, part of it going around the field and part around the armature. Another type, called series-

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