Electricity

in physics, a cause the nature of which is as yet largely unknown. Under certain circumstances it produces heat, light, chemical action, attraction, or repulsion. It is in turn set in operation by them. The results last named are also called forms of electricity, so that the term applies not only to the cause, whatever that may be, but to its manifestations as well. There is deep interest in a recently propounded theory that terrestrial electricity, like heat and light, reaches us from the sun; and that the difference between heat and light, on the one hand, and electricity or magnetism, on the other, is one of wave length and frequency. According to this theory, heat, light, electricity, and magnetism are much the same. Shorten the wave length of heat and we have light; shorten the wave length of light and we have electricity; increase the wave length of electricity, that is to say, retard its movement and we have heat or light. It is difficult to reconcile all electrical phenomena with this theory; but it is fascinating, and gives hope of clearing up what has hitherto been considered a mysterious subject. Electricity has been discussed as though it were a fluid. If the modern theory should prevail, such terms as current and pressure would seem a little unfortunate.

Up to the present time, electricity has been considered as of two kinds,--that excited by friction and that generated by chemical action, or by a dynamo. The discovery of frictional or static electricity is attributed usually to Thales, who flourished in the sixth century B. C. He observed that amber rubbed by silk had the peculiar property of attracting bits of pith, paper, husk, or other light bodies. Many other substances, such as glass, sulphur, and resin, may be electrified in like manner. The electricity produced in the glass is called vitreous or positive electricity; while that of the silk with which it is rubbed is called resinous or negative. If a stick of sealing wax be rubbed with silk, however, the electricity developed in the silk is positive; that in the wax, negative. Many interesting experiments may be conducted with frictional electricity.

The so-called Leyden jar consists essentially of two sheets of tinfoil, separated by a non-conducting glass. The sheets may be charged with opposite kinds of electricity in such a way as to obtain quite a spark on uniting the two surfaces by a conductor. The Holtz machine is a device for generating electricity by causing a disk of glass to rotate rapidly through a rubber. It produces a series of electric sparks. Ordinary lightning is due to a discharge of static electricity stored up in a cloud. The earth serves for the second surface. The air serves to separate them. Little practical use has been found for static electricity in the arts and sciences.

So-called current electricity may be produced in various ways. The most common means is that of chemical action in a voltaic battery. Electricity may also be generated by revolving a coil of wire in the field between the poles of a magnet, as in the case of the dynamo electric machine. If two pieces of different metals, as bismuth and antimony, be connected at one end by a copper wire, and be soldered together at the other, an electrical current may be produced in the wire by a change of temperature, that is, by heating or cooling the soldered point.

The effects of electricity are numerous and of great importance in the industrial world. The electricity used in electrotyping, and electrolysis, in operating telegraph lines, ocean cables, doorbells, clocks, and many other contrivances is developed usually by a battery. That used in operating an electric light plant, in propelling trolley cars, and in operating machinery generally is derived usually from a dynamo,--an electric machine, which, in turn, is set in motion by the consumption of fuel or by water power. It should be remembered in all cases that the dynamo and motor are unable to create electricity. The motive power must in every case spring from the chemical action, the consumption of fuel, or some mechanical work, such as that performed by falling water or the turning of a crank by hand or horse power. One, and, in fact, the great advantage derived from a dynamo is the transmission of power without serious loss or inconvenience to great distances. Enormous dynamos at Niagara Falls, in California, and elsewhere are enabled to send power through cables to cities miles away. Where the work is to be done on the spot, as in the case of a grist mill, it is quite as well to connect the mill by belt with the shaft of a water wheel; but, when it is desired to do work at a distance, the falling water may be used to rotate a dynamo. The electricity thus generated may be transmitted to great distances, far beyond the reach of shaft and belt. Mexico now has the longest electrical transmission line on record. Electricity developed by a mountain torrent is conveyed 95 miles to the capital city with a loss of but six per cent. The line continues 86 miles farther to a mining plant, 181 miles in all. A six-strand copper cable is suspended on steel towers instead of poles. The line cost $10,000 per mile and carries 60,000 volts.

Edison is of the opinion that coal should be converted into electricity by huge powerhouses situated at the mines. Coal is valued at about a dollar a ton at the mouth of the mine. Edison claims that steam engines, dynamos, and wire conductors can convert the heat of coal into electrical energy and deliver it thousands of miles away at a fraction of the present cost of freight. All the work of heating and lighting, and the propelling of machinery in factories and mills, now done by coal, may be done by coal-generated electricity, thus saving the hauling and handling of coal and the dust and smoke now accompanying its use. By the use of storage batteries, all vehicles, especially in cities, may be run without the aid of horses. He deems it quite possible to banish the horse stable from the city. The great objection to electricity for railways seems to be that a single break in the transmission apparatus may tie up a whole system.

There is a widespread impression that the end of the nineteenth century witnessed the development of a new power. It is a mistake, however, to say that any part of the world's work is done by electricity, but rather that electricity is a convenient means of applying power. A bulletin, issued in 1904, made the following statements.

Four billion dollars is the present capitalization of the corporations in the United States that are engaged in the design, construction or operation of electrical machinery. Telephone subscribers number 7,000,000, and there are 5,000,000 miles of telephone wires in the country; one system reports 2,700,000,000 conversations for a single year, and 44,000 persons employed. The wires of one telegraph company would reach five times to the moon. Last year this company sent 69,790,866 messages, exclusive of 10,000,000 leased wire and railway messages; and two telegraph companies together maintain 43,000 offices. The number of 16 candle power incandescent lamps in the United States is 31,000,000, and the aggregate electrical horse power is 15,660,000. The United States Census Report, dated June, 1902, shows 22,589 miles of electric railways in operation, using 67,199 cars, and requiring 1,298,133 horse power. The total number of passengers carried for that year was 6,000,000,000, and the gross earnings were about $242,000,000. In electrical manufacturing concerns, exclusive of sales departments, are employed 55,000 persons.

This enormous industry is but thirty years old, and it is rapidly growing. The increase in the sale of electrical energy for lighting, electrochemical and power purposes has been for each of the past few years over twenty per cent above that of each preceding year.

See Telephone; Telegraph; Light; Heat