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. |
| α, β, | Angle. |
| 3. Derived Mechanical. | |
| v, | Velocity. |
| ω, | Angular velocity. |
| r, | Momentum. |
| a, | Acceleration. |
| g, | Acceleration due to gravity = 32.2 feet per second. |
| F, f, | Force. |
| W, | Work. |
| P, | Power. |
| δ, | Dyne. |
| ε, | Ergs, |
| 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. |
| φ, | Magnetic flux. |
 , | Magnetic flux density or magnetic induction. |
| , | Magnetizing force. |
 , | Magnetomotive force. |
 , | Reluctance, magnetic resistance. |
| μ, | Magnetic permeability. |
| κ, | Magnetic susceptibility. |
| ν, | 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. |
| P, | Electric power, watt; kilowatt. |
| p, | Resistivity (specific resistance) ohm centimeter. |
| G, | Conductance, mho. |
| γ, | 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 = 3×1010 centimeters per second approximately. |
| 7. Symbols in general use. | |
| D, | Diameter. |
| r, | Radius. |
| t, | Temperature. |
| θ, | Deflection of galvanometer needle. |
| N, n, | Number of anything. |
| π, | Circumference ÷ diameter = 3.141592. |
| ω, | 2πf = 6.2831 × frequency, in alternating current. |
| ~, f, | Frequency, periodicity, cycles per second. |
| φ, | 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. |