Turns, Secondary Ampere-.

The ampere-turns on the secondary circuit of an induction coil or transformer. These depend on the path provided for the current. If of negligible inductance, such as a number of incandescent lamps would provide, the ampere-turns should be equal to those of the primary coil.

(See Turns, Primary Ampere.)

Typewriter, Electric.

A typewriter in which the work of printing or of pressing the type faces against the paper, or printing ribbon, is done by electro-magnetic attraction. The keys close electric circuits, throwing the electro-magnetic action into play. This involves the use of electricity for what is ordinarily only a mechanical process. The strength of the impression, however, is independent of the touch of the operator. It has not come into very extensive use.

[Transcriber's note: IBM introduced widely used electric typewriters in 1935.]

Ultra-gaseous Matter.

Gas so rarefied that its molecules do not collide or very rarely do so.

Experiments of very striking nature have been devised by Crookes and others to ill.u.s.trate the peculiar phenomena that this matter presents.

The general lines of this work are similar to the methods used in Geissler tube experiments, except that the vacua used are very much higher.

When the vacuum is increased so that but one-millionth of the original gas is left the radiant state is reached. The molecules in their kinetic movements beat back and forth in straight lines without colliding, or with very rare collisions. Their motions can be guided and rendered visible by electrification. A tube or small gla.s.s bulb with platinum electrodes sealed in it, is exhausted to the requisite degree and is hermetically sealed by melting the gla.s.s. The electrodes are connected to the terminals of an induction coil or other source of high tension electrification. The molecules which come in contact with a negatively electrified pole are repelled from it in directions normal to its surface. They produce different phosph.o.r.escent or luminous effects in their mutual collisions.

Thus if they are made to impinge upon gla.s.s, diamond or ruby, intense phosph.o.r.escence is produced. A piece of platinum subjected to molecular bombardment is brought to white heat. A movable body can be made to move under their effects. Two streams proceeding from one negative pole repel each other. The stream of molecules can be drawn out of their course by a magnet.

The experiments are all done on a small scale in tubes and bulbs, resembling to a certain extent Geissler tubes.

[Transcriber's note: These effects are caused by plasma--ionized gas and electrons.]

552 STANDARD ELECTRICAL DICTIONARY.

Unbuilding.

The loss of its charge or excitation by a self-exciting dynamo. It is the reverse of building-up. The latter indicates the exciting of the field by the action of the machine itself; the former the spontaneous loss of charge on open circuit or from other cause.

Underground Conductor.

An electric conductor insulated and placed under the surface of the earth, as distinguished from aerial conductors.

Underground Electric Subway.

A subway for the enclosing of electric telegraph and other conductors under the surface, generally in the line of streets, to do away with telegraph poles and aerial lines of wire. Many systems have been devised. The general type includes tubes called ducts in sets, called conduits, bedded in concrete or otherwise protected. Every two or three hundred feet the sets lead into a cistern-like cavity called a manhole.

The insulated wires or cables, generally sheathed with a lead alloy are introduced into the tubes through the man-holes. A rope is first fed through the tube. To do this short rods which screw together are generally employed. One by one they are introduced, and each end one is screwed to the series of rods already in the duct. When the end of the duct is reached the rope is fastened to the last rod, and the rods are then drawn through, unscrewed one by one and removed, the rope following them. By means of the rope a windla.s.s or capstan may be applied to draw the cable into the duct. At least at every second man-hole the cables have to be spliced.

Each cable may contain a large number of conductors of small size for telephoning, or a smaller number for electric light and power. The tendency is now to separate the different cla.s.ses of wires in important lines, placing the heavier wires on one side of the street and the telephone and telegraph wires on the other. This of course necessitates two separate conduits.

The advantage of underground distribution affects not only the appearance of streets in doing away with unsightly telegraph poles, but it also removes an element of danger at fires. Aerial wires interfere greatly with the handling of ladders at fires, and expose the firemen who attempt to cut them to danger to their lives from shock.

533 STANDARD ELECTRICAL DICTIONARY.

Unidirectional. adj.

Having one direction as a "unidirectional current" or "unidirectional leak." The term is descriptive, and applicable to many cases.

Uniform. adj.

Unvarying; as a uniform potential difference, uniform current or conductor of uniform resistance per unit of length. The term is descriptive, and its application and meaning are obvious.

Uniform Field of Force.

A field of evenly distributed force; one in which the number of lines of force per unit of area of any equipotential surface is the same.

Unipolar. adj.

Strictly speaking this term means having only one pole, and is applied to magnets, armatures and the like. In its use a solecism is involved, for there is no such condition possible as unipolar magnetism or distribution of magnetism. An example of its use is shown in unipolar magnets. (See Magnet, Unipolar.)

Unipolar Armature.

An armature of a unipolar dynamo; an armature whose windings continuously cut the lines of force about the one pole, and hence whose polarity is unchanged in its rotation.

Unipolar Current Induction.

Current induction produced by moving a conductor through a magnetic field of force so that it always cuts the lines in similar relation to itself. Thus it produces a constant current through its own circuit, if a closed one, and no commutator is required. As this case always in practice amounts to the cutting of lines of force in the neighborhood of a single pole the term unipolar is employed to designate the action.

The simplest representation of unipolar induction is the rotating of a conductor around the end of a bar magnet, its axis of rotation corresponding with the axis of the magnet.

Unipolar Dynamo.

A dynamo in which one part of the conductor slides on or around the magnet, so as always to cut lines of force near the same pole of the magnet.

Unit.

A directly or indirectly conventional and arbitrary quant.i.ty, in terms of which measurements of things with dimensions expressible in the chosen units are executed.

Thus for length the c. g. s. unit is the centimeter; the B. E. unit is the foot.

554 STANDARD ELECTRICAL DICTIONARY.

Unit, Absolute.

A unit based on the three fundamental units of length, ma.s.s and time.

These units are the centimeter, gram and second. Each one in itself may be termed a fundamental absolute unit. The system of such units is termed the centimeter-gram-second system.

Unit, Angle.

A factor or datum in angular velocity, q. v. It is the angle subtended by a portion of the circ.u.mference equal in length to the radius of the circle. It is equal very nearly to 57.29578? or 57? 17' 44.8".

Unit, B. A.

This term, while logically applicable to any of the British a.s.sociation units, is often restricted to the ohm as formerly defined by the British a.s.sociation, the B. A. Unit of Resistance, q. v.