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generating electricity and distributing it to houses and factories have been established, the application of the electric current to motive purposes will come more and more into fashion. A hundred little services will be performed by it which are now done by manual labour or by steam and other sources of power. The same wires which convey the current for lighting the rooms of a home will serve to deliver it for driving the sewing-machine or grinding the coffee. Moreover, a mechanic or watchmaker will be able to drive his lathe by it; and it is probable that the old habit of craftsmen working at home will be to some extent revived, since it will be possible to have power brought there like gas or water. The great economy of very
very large steam-engines over small ones has led to the development of large factories, where hundreds of human beings are cooped up amid the ncessant roar of machinery and the stifling dust of a polluted atmosphere. But when power has been distributed by wire to this place and to that, a blow will have been struck at this imprisonment of men and women in the interests of capital, and the consequent deterioration of their souls and bodies. That power on a large scale can be distributed in this way has been already demonstrated, and Sir William Thomson, amongst others, has shown that the cost for conductors capable of transmitting hundreds of horse-power need not be excessive. He even proposes to utilise some of the power of Niagara Falls to light the towns and drive the mills for a hundred miles around. Whether this be done or not, it is certain that the power of waterfalls in hilly countries, which is now largely wasted, will be utilised for electric light and motive purposes.
All Glasgow, for instance, could be lighted by the Falls of Clyde, and many of the great steam-hammers in its shipyards driven to boot. Wind, too, will be utilised as a primary source of electric power; for, though variable and inconstant, it can be made to turn dynamos which will store the electricity they generate in accumulators, from which a constant current can be obtained. The intermittent power of the tides and of river floods may also be turned to account in a similar way; even the induced currents of the atmosphere in lightning-rods may be stored up, as well as the currents generated in thermo-piles by the solar heat, and thus we shall have the light of day made captive for the uses of the night, and the very lightning flash submitted to the services of man.
ELECTRIC HEA T.
We have already stated that the electric current is capable of producing heat as well as light. Indeed, the electric light is due to the high temperature which is excited either in the vapours of the luminous arc or the incandescent filament of a lamp by the passage
of the current through it: and the reason why an electric lamp does not give off much heat is that the heated mass is very small. The temperature of the arc is high enough to fuse platinum or steel, but the body of matter carrying the heat is only a puff of carbon dust. Again, the filament of an incandescent light is raised to a temperature of over 1000° Fah., but it weighs only a few grains. It is possible, however, by both these means to generate a quantity of heat sufficient for useful purposes.
. By employing powerful currents and massy carbonrods, Dr. C. W. Siemens has applied the electric arc to the fusion of metals. He has in fact constructed an electric furnace, which is illustrated in Fig. 78. It consists of a fire-clay furnace, having a plumbago crucible inside. A short carbon rod enters the bottom of this crucible by a hole, and serves as the positive electrode of the current, that is to say, the carbon
connected to the positive pole of the electric generator. Through the lid, which is slightly raised in the sketch, a corresponding carbon rod, serving as the negative electrode, enters the crucible. This rod, or rather bundle of rods, is suspended from one end of a balance beam, from the other end of which hangs a soft iron rod, which enters the hollow of a coil or bobbin of insulated copper wire. The lower part of this iron core dips into a well of glycerine or other viscous liquid, so that it will have a smooth motion up and down when the balance beam moves. A movable weight serves to balance the beam so as to give a proper length of arc between the two carbon rods in the crucible. The current is conveyed to the two carbons by wires, and the arc established by it is so powerful that comparatively large masses of copper, platinum, nickel, and tungsten, as well as the most refractory earths, are in a short time fused by it. The furnace is rendered self-regulating by connecting the solenoid or bobbin in a derived circuit or by-path from the arc, so that a portion of the current is diverted through it. Then if the arc becomes too long, and its resistance too great, more of the current is diverted through the solenoid, and this sucks up the soft iron core into the bobbin, thereby raising that end of the balance beam and lowering the other which carries the upper carbon. The arc is thus shortened again to its normal length. Contrarily, if the arc becomes too short, and its resistance consequently diminished, less current flows in the solenoid and the core sinks, pulling down the beam at its own end and raising the carbon at the other.
In this electric furnace Dr. Siemens can melt several pounds of old files in fifteen minutes with the current