action--magnetic vibrators--vibrator adjustment--table of induction coil dimensions--table of sparking distances in air--points relating to induction coils--wiring diagram.2
THE DYNAMO 155 to 160
Operation--essential parts--field magnets--armature--construction of dynamos--parts; bed plate, field magnets, armature, commutator, brushes.
THE DYNAMO: BASIC PRINCIPLES 161 to 170
Definitions--essential parts--elementary alternator--operation--direction of induced current--application of Fleming's rule--cy-
cle of operation--the sine curve; its construction and application.
THE DYNAMO: CURRENT COMMUTATION 171 to 180
How the current is produced--how direct current is obtained--the commutator--inductors--"continuous current"--action of four
coil elementary dynamo--conditions for steadiness of the current. CLASSES OF DYNAMO 181 to 198
Classification--bipolar and multi-polar dynamos--difference between dynamo and magneto--self-exciting dynamo--the series dy-namo--regulation of series dynamo; difficulties experienced--the shunt dynamo--adaptation--operation--characteristic--regulation--the compound dynamo--service intended for--regulation--over compounding--usual degree of over compounding--short shunt--long shunt--voltage of short and long shunt machines--separately excited dynamos--Dobrowolski three wire dynamo. FIELD MAGNETS 199 to 220
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
