Object--essential parts--classes of field magnet--multi-polar field magnets--construction--choice of materials--design--pole pieces--eddy current--laminated fields--construction to reduce reluctance of the magnetic circuit--magnetizing coils--methods of winding--coil ends--insulation--attachment of coils--coil connections--heating--ventilation.
INTRODUCTORY CHAPTER
The subject matter of this work relates to one of the secrets of creation which appears to have been intended at the very beginning to be "sought out." This idea is expressed in a certain saying copied three or four thousand years ago by the men of Hezekiah, King of Judah: from Solomon's proverbs: "It is the glory of God to conceal a thing: But the glory of Kings (i.e., wise men), to search out a matter."
In all that may be said hereafter through the work, it is admitted that the results recorded are the determinations of experiments performed by an incredible number of searchers extending through many ages. These inquiries have been pursued with a generous rivalry which has permitted discovery to be added to discovery, until the sum total has been wrought into such exactness that it has been thoughtlessly stated that there is nothing more, save its application.
It may be well, however, to state a few fundamental facts relating to electricity: 1, Electricity and magnetism are one and the same thing; 2, what is really known about it has come as a discovery and not as an invention. Thus, we say the intrepid explorer discovered the pole, not that he invented it. So with electricity it has been a subject of discovery while its many applications to useful purposes have been veritable inventions; 3, the earth itself is a magnet.
This last is shown by the fact that the earth affects a magnet just as one magnet affects another. Magnets are bodies, either natural or artificial, which have the property of attracting iron, and the power, when freely suspended, of taking a direction toward the poles of the earth. The natural magnet is sometimes called the loadstone. This word is said to be derived from loedan, a Saxon word which signifies to guide. It is an oxide of iron of a peculiar character, found occasionally in beds of iron ore. Though commonly met with in irregular masses only a few inches in diameter, however, loadstones of larger sizes are sometimes found.
By means of simple experiments it may be ascertained that the magnet has the following general properties, viz: 1, power of attraction; 2, power of repulsion; 3, power of communicating magnetism to iron or steel; 4, polarity, or the power of taking a direction toward the poles of the earth; 5, power of inclining itself toward a point below the horizon.
Speaking generally we may say, that magnetism is a department of electrical science which treats of the properties and effects of the magnet. The same terms are also used to denote the unknown cause of magnetic phenomena, as when we speak of magnetism as excited, imparted, and so on.
Lightning and the Northern Lights are displays of electricity on a grand scale. Electricity is a term derived from the Greek word for
amber, that being the substance in which a property of the agent now denominated electricity was first observed.
The ancient Greek philosophers were acquainted with the fact that amber, when rubbed, acquired the property of attracting light
bodies; hence the effect was denominated electrical and in later times, the term electricity has been used to denote the unknown cause of electrical phenomena, and broadly the science which treats of electrical phenomena and their causes.
Electricity, whatever it may prove to be, is not matter nor is it energy; it is however a means or medium of transmitting energy.
If electricity is to transmit or convey energy along a wire, this energy must be imparted to the electricity from some external source,
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that is to say, before electricity can perform any work it must be set in motion, against more or less resistance. This involves that pressure must be applied, and to obtain this pressure, energy must be expended from some external source.
Accordingly, in electrical engineering, the first principle to be grasped is that of energy. Without the expenditure of energy no useful
work can be accomplished.
Energy may be defined as the capacity for performing work.
Although electricity is not energy, electricity under pressure is a form of energy spoken of as electrical energy.
In an expenditure of energy in this form, the electricity acts simply as a transmission agent or medium to transmit the energy im-
parted to it in causing it to flow.
In a similar manner, steam acts as a transmission agent or medium to transmit the heat energy of the coal to the steam engine, where it is converted into mechanical energy.
As just stated, electricity under pressure is a form of energy, and its generation is simply a transformation of energy from one form into another. Usually, mechanical energy is converted into electrical energy, and a dynamo is employed for effecting the transformation.
In transforming the mechanical energy of waterfalls into electric energy, this natural power of water due to its weight and motion is
first converted into rotary motion by a turbine or water wheel, and then converted into electric energy by a dynamo, or an alternator.
All dynamos are but machines for converting into electric energy the energy which is given to them by some prime mover, as a steam engine, a gas engine, by hydraulic or even by wind power.
All electric motors are merely machines for reconverting the electric energy which they receive by means of the conducting wires or mains, into mechanical energy.
All electric lamps are contrivances for converting into luminous energy a percentage of the electric energy that is supplied through the mains.
Potential and Kinetic Energy.--Potential energy is the capacity for performing work which a body possesses by virtue of its position. Kinetic energy is the capacity for performing work which a body possesses by virtue of its motion.
It must be evident that position or motion given to a body enables it to perform work. In the first instance, for example, a heavy weight at the top of a high tower possesses potential energy. A ten pound weight supported one foot above a plane has ten foot pounds of potential energy.
The flywheel of a steam engine in motion is an example of a body possessing kinetic energy. Some of this kinetic energy which was stored up in the fly wheel during the working stroke is expended in moving the engine over the "dead center," and any other point where no torque is produced by the pressure on the piston.
Chemical Energy can be converted into electric energy to a limited extent by means of the electric battery, but the cost of this en-ergy is so high that it is commercially feasible only where small quantities are required, and the cost of production is secondary to the convenience of generation, as for signalling purposes, the operation of bells and annunciators, etc. The chemical energy of coal and other fuels cannot be directly converted into electric energy. For power producing purposes, the chemical energy of a fuel is first converted into heat by combustion, and the heat thus obtained converted into mechanical energy by some form of heat engine, and the mechanical energy subsequently transformed into electric energy in an electric generator. Energy cannot be created or destroyed. This is the law known as the conservation of energy which has been built up by Helmholtz, Thomson, Joule and others. It teaches further, that energy can be transmitted from one body to another or transformed in its manifestations. Energy may be dissipated, that is, converted into a form from which it cannot be recovered, as is the case with the great percentage of heat escaping from the exhaust nozzle of a locomotive or in the circulating water of a steamship, but the total amount of energy in the universe, it is argued, remains constant and invariable. 4 Following