Fig. 117. CHARACTERISTIC CURVE OF ALTERNATING CURRENT.

160 STANDARD ELECTRICAL DICTIONARY.

Current, Atomic.

A unit of current strength used in Germany; the strength of a current which will liberate in 24 hours (86,400 seconds) one gram of hydrogen gas, in a water voltameter. The atomic current is equal to 1.111 amperes. In telegraphic work the milliatom is used as a unit, comparable to the milliampere. The latter is now displacing it.

Current, Charge.

If the external coatings of a charged and uncharged jar are placed in connection, and if the inner coatings are now connected, after separating them they are both found to be charged in the same manner. In this process a current has been produced between the outside coatings and one between the inner ones, to which Dove has given the name Charge Current, and which has all the properties of the ordinary discharge current. (Ganot.)

Current, Circular.

A current pa.s.sing through a circular conductor; a current whose path is in the shape of a circle.

Current, Commuted.

A current changed, as regards direction or directions, by a commutator, q. v., or its equivalent.

Current, Constant.

An unvarying current. A constant current system is one maintaining such a current. In electric series, incandescent lighting, a constant current is employed, and the system is termed as above. In arc lighting systems, the constant current series arrangement is almost universal.

161 STANDARD ELECTRICAL DICTIONARY.

Current, Continuous.

A current of one direction only; the reverse of an alternating current.

(See Current, Alternating.)

Current, Critical.

The current produced by a dynamo at its critical speed; at that speed when a slight difference in speed produces a great difference in electro-motive force. On the characteristic curve it corresponds to the point where the curve bends sharply, and where the electro-motive force is about two-thirds its maximum.

Current, Daniell/U.S. , Daniell/Siemens' Unit.

A unit of current strength used in Germany. It is the strength of a current produced by one Daniell cell in a circuit of the resistance of one Siemens' unit. The current deposits 1.38 grams of copper per hour.

It is equal to 1.16 amperes.

Current, Demarcation.

In electro-therapeutics, a current which can be taken from an injured muscle, the injured portion acting electro-negatively toward the uninjured portion.

Current Density.

The current intensity per unit of cross-sectional area of the conductor.

The expression is more generally used for electrolytic conduction, where the current-density is referred to the mean facing areas of the electrodes, or else to the facing area of the cathode only.

The quality of the deposited metal is intimately related to the current density. (See Burning.)

Proper Current Density for Electroplating Amperes Per Square Foot of Cathode.--(Urquhart.) Copper, Acid Bath. 5.0 to 10.0 " Cyanide Bath, 3.0 " 5.0 Silver, Double Cyanide, 2.0 " 5.0 Gold, Chloride dissolved in Pota.s.sium Cyanide, 1.0 " 2.0 Nickel, Double Sulphate, 6.6 " 8.0 Bra.s.s, Cyanide, 2.0 " 3.0

Current, Diacritical.

A current, which, pa.s.sing through a helix surrounding an iron core, brings it to one-half its magnetic saturation, q. v.

Current, Diaphragm.

If a liquid is forced through a diaphragm, a potential difference between the liquid on opposite sides of the diaphragm is maintained.

Electrodes or terminals of platinum may be immersed in the liquid, and a continuous current, termed a diaphragm current, may be taken as long as the liquid is forced through the diaphragm. The potential difference is proportional to the pressure, and also depends on the nature of the diaphragm and on the liquid.

162 STANDARD ELECTRICAL DICTIONARY.

Current, Direct.

A current of unvarying direction, as distinguished from an alternating current. It may be pulsatory or intermittent in character, but must be of constant direction.

Current, Direct Induced.

On breaking a circuit, if it is susceptible of exercising self-induction, q. v., an extra current, in the direction of the original is induced, which is called "direct" because in the same direction as the original. The same is produced by a current in one circuit upon a parallel one altogether separated from it. (See Induction, Electro-Magnetic-Current, Extra.)

Synonym--Break Induced Current.

Current, Direction of.

The a.s.sumed direction of a current is from positively charged electrode to negatively charged one; in a galvanic battery from the carbon or copper plate through the outer circuit to the zinc plate and back through the electrolyte to the carbon or copper plate. (See Current.)

[Transcriber's note: Current is caused by the motion of negative electrons, from the negative pole to the positive. The electron was discovered five years after this publication.]

Current, Displacement.

The movement or current of electricity taking place in a dielectric during displacement. It is theoretical only and can only be a.s.sumed to be of infinitely short duration. (See Displacement, Electric.)

Currents, Eddy Displacement.

The a.n.a.logues of Foucault currents, hypothetically produced in the ma.s.s of a dielectric by the separation of the electricity or by its electrification. (See Displacement.)

Current, Extra.

When a circuit is suddenly opened or closed a current of very brief duration, in the first case in the same direction, in the other case in the opposite direction, is produced, which exceeds the ordinary current in intensity. A high potential difference is produced for an instant only. These are called extra currents. As they are produced by electro-magnetic induction, anything which strengthens the field of force increases the potential difference to which they are due. Thus the wire may be wound in a coil around an iron core, in which case the extra currents may be very strong. (See Induction, Self-Coil, Spark.)

Current, Faradic.

A term in medical electricity for the induced or secondary alternating current, produced by comparatively high electro-motive force, such as given by an induction coil or magneto-generator, as distinguished from the regular battery current.