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.