this law comes the doctrine of the conservation of electricity as announced by Lippman, being undoubtedly the outcome of the ideas of Maxwell and of Faraday as to the nature of electricity. According to their doctrine, electricity cannot be created or destroyed, although its distribution may be altered. Lippman states that every charge of electricity has an opposite and equal charge somewhere in the universe more or less distributed; that is, the sum of positive charges is always equal to the sum of negative charges. In altering the distribution of electricity, we may cause more to appear at one place and less at another, or may change it from the condition of rest to that of motion, or may cause it to spin round in whirlpools or vortices, which themselves can attract or repel other vortices. According to this view all our electrical machines and batteries are merely instruments for altering the distribution of electricity by moving some of it from one place to another, or for causing electricity, when accumulated or heaped, together in one place, to do work in returning to its former distribution. Electrical engineering has developed largely and widely within a very short time and its many applications has created so great a demand for various kinds of electrical apparatus, that their manufacture forms one of the leading industries. Electricity is very valuable as a medium for the transmission of energy, especially to long distances; it is also used to great advantage in lighting, being free from the disagreeable properties of gas or oil. Again, electricity finds various applications, in extracting gold from the ore, pumping and ventilation of mines, traction, telephone, telegraph, electroplating, therapeutics,
etc. These few, of its many applications will perhaps serve to indicate the far reaching interest and importance of electricity, and possibly help to kindle in the student something of the eagerness in his work and enthusiasm without which he will fail to do justice either to his calling or to himself. SIGNS AND SYMBOLS The following signs, symbols and abbreviations are almost universally employed in descriptive and technical works on electrical subjects. Although, in the arrangement of the Guides, the direct current and alternating current matter has been kept separate, it is perhaps advisable in the case of signs and symbols, to combine those relating to the alternating current with the direct current and other symbols, making a single table, rather than have them scattered throughout the work. 1. Fundamental. l, Length. cm. = centimeter; in., or '' = inch, ft. or '' = foot. M, Mass. gr. = mass of 1 gramme kg. = 1 kilogramme. T, t, Time, s = second. 2. Derived Geometric. S, s, Surface. E, Volume. '', '', Angle. 3. Derived Mechanical. v, Velocity. '', Angular velocity. r, Momentum. a, Acceleration. g, Acceleration due to gravity = 32.2 feet per second. F, f, Force. W, Work. P, Power. '', Dyne. '', Ergs, 5 ft. lb., Foot pound. H.P., h.p. Horse power. I.H.P., Indicated horse power. B.H.P., Brake horse power. E.H.P., Electrical horse power. J, Joule's equivalent. p, Pressure. K, Moment of inertia. 4. Derived Electrostatic. e, Pressure difference. i, Current. r, Resistance. q, Quantity. c, Capacity. sc, Specific inductive capacity. 5. Derived Magnetic. m, Strength of pole. , Intensity of magnetization. , Magnetic moment. , Horizontal intensity of earth's magnetism. , Field intensity. '', Magnetic flux. , Magnetic flux density or magnetic induction. , Magnetizing force. , Magnetomotive force. , Reluctance, magnetic resistance. m, Magnetic permeability. '', Magnetic susceptibility. '', Reluctivity (specific magnetic resistance). 6. Derived Electromagnetic. R, Resistance, ohm. O, do, megohm. E, Volt, pressure. Eim Impressed pressure. Ea, Eo Active pressure; ohmic drop. Ev Virtual pressure. Emax Maximum pressure. Eav Average pressure. Eef Effective pressure. Ei Inductance pressure. Ec Capacity pressure. U, Difference of pressure, volt. I, Intensity of current, ampere. Iim Impressed current. Ia Active current. Iv Virtual current. Imax Maximum current. Iav Average current. Ief Effective current. Q, Quantity of electricity, ampere-hour; coulomb. C, Capacity, farad. W, Electric energy, watt-hour; Joule. 6 P, Electric power, watt; kilowatt. p, Resistivity (specific resistance) ohm centimeter. G, Conductance, mho. '', Conductivity (specific conductivity). Y, Admittance, mho. Z, Impedance, ohm. X, Reactance, ohm. Xi Inductance reactance. Xc Capacity reactance. B, Susceptance, mho. L, Inductance (coefficient of Induction), henry. v, Ratio of electromagnetic to electrostatic unit of quantity = 3x1010 centimeters per second approximately. 7. Symbols in general use. D, Diameter. r, Radius. t, Temperature. '', Deflection of galvanometer needle. N, n, Number of anything.
p, Circumference / diameter = 3.141592.
'', 2pf = 6.2831 x frequency, in alternating current.
~, f, Frequency, periodicity, cycles per second.
'', Phase angle.
G, Galvanometer.
S, Shunt.
N, n, North pole of a magnet. S, s, South pole of a magnet. A.C. Alternating current.
D.C. Direct current.
P.D. Pressure difference. P.F. Power factor.
C.G.S. Centimeter, Gramme, Second system. B.&S. Brown & Sharpe wire gauge.
B.W.G. Birmingham wire gauge. R.p.m. Revolutions per minute. C.P. Candle power.
, Incandescent lamp.
, Arc lamp.
, OR , Condenser.
, Battery of cells.
, Dynamo, or direct current motor.
, Alternator, or alternating current motor.
, Converter.
, Static transformer.
, Inductive resistance.
, Non-inductive resistance.
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CHAPTER I ELECTRICITY
Nature and Source of Electricity.--What is electricity? This is a question that is frequently asked, but has not yet been satisfactorily answered. It is a force, subject to control under well known laws.
While the nature and source of electricity still remain a mystery, many things about it have become known, thus, it is positively as-sured that electricity never manifests itself except when there is some mechanical disturbance in ordinary matter.
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The true nature of electricity has not yet been discovered. Many think it a quality inherent in nearly all the substances, and accompanied by a peculiar movement or arrangement of the molecules. Some assume that the phenomena of electricity are due to a peculiar state of strain or tension in the ether which is present everywhere, even in and between the atoms of the most solid bodies. If the latter theory be the true one, and if the atmosphere of the earth be surrounded by the same ether, it may be possible to establish these assumptions as facts.
The most modern supposition regarding this matter, by Maxwell, is that light itself is founded on electricity, and that light waves are merely electromagnetic waves. The theory "that2 electricity is related to, or identical with, the luminiferous ether," has been accepted by the most prominent scientists.
But while electricity is still a mystery, much is known about the laws governing its phenomena. Man has mastered this mighty force and made it his powerful servant; he can produce it and use it.
Electricity, it is also conceded, is without weight, and, while it is without doubt, one and the same, it is for convenience sometimes
classified according to its motion, as:
1. Static electricity, or electricity at rest;
2. Current electricity, or electricity in motion;
3. Magnetism, or electricity in rotation;
4. Electricity in vibration (radiation).
Other useful divisions are:
1. Positive;
2. Negative electricity;
3. Static;
4. Dynamic electricity.
Static Electricity.--This is a term employed to define electricity produced by friction. It is properly employed in the sense of a static
charge which shows itself by the attraction or repulsion between charged bodies.
When static electricity is discharged, it causes more or less of a current, which shows itself by the passage of sparks or a brush discharge; by a peculiar prickling sensation; by a peculiar smell due to its chemical effects; by heating the air or other
