Electrical contact

“ If the tube be exhausted of air, a non electric lining in contact with the wire is not necessary; for in vacuo, the electrical fire will fly freely from the inner surface, without a non-electric conductor: but air resists its motion; for being itself an electric per se, it does not attract it, having already its quantity. ”

“ In discharging electrical jars, the electricity goes in the greatest quantity through the best conductors, and by the shortest passage. Thus if a chain and a wire be made to communicate at the same time with the outer coating of a jar, and be both presented to the knob of that jar, the greater part of the charge will pass by the wire, and very little by the chain, because the latter is a worse conductor than the former, on account of its discontinuation at every link. When the discharge is 29made by the chain only, sparks are seen at every link, which is a proof they are not in contact. ”

“ Form a communication by a chain from the coating to the cushion, and the phial will charge.
For the globe then draws the electrical fire out of the outside surface of the phial, and forces it, through the prime conductor and wire of the phial, into the inside surface. ”

“ Why when the telegraph was first invented it was necessary to double the wire lines, putting up two wires every time by way of completing the circuit. You know electrical energy will not manifest itself, or as we say, the electric current will not flow, unless there is a circuit established. ”

“ Fig. 22 shows the form of apparatus that I was then employing for producing undulatory currents of electricity for the purposes of multiple telegraphy. A steel reed A was clamped firmly by one extremity to the uncovered leg h of an electro-magnet E, and the free end of the reed projected above the covered leg. When the reed A was vibrated in any mechanical way, the battery current was thrown into waves, and electrical undulations traversed the circuit B E W E ́, throwing into vibration the corresponding reed A ́ at the other end of the circuit. ”

“ The term wiring is commonly understood to mean the methods employed in laying the conductors used for the transmission and distribution of electrical energy for lighting, power, and other purposes. Interior wiring, comprises the various methods of installing the conductors from the entrance devices in the walls or other parts of the buildings to the lamps, motors, and other electrical apparatus within the buildings. ”

“ How quickly a spoon inserted into a hot cup of tea becomes uncomfortably hot, though the hand can be held very close to the liquid without feeling more than a gentle warmth. And we all have noticed that the very least air-gap in an electric circuit effectively breaks a current capable of traversing miles of wire. If the current is so intense that it insists on passing the gap, it leaps across with a report, making a spark that is at once intensely bright and hot. Metal wires are to electricity what speaking tubes are to sound; they are as it were electrical tubes through the air and ether. ”

“ To exhibit this mysterious effect we bring the ends of the electrical current which we wish to excite near each other, but not touching, in a glass tube with thin walls, from which the air has been exhausted. When the X rays fall on the gap between the wires the electrical current immediately jumps across the gap with a vivid light. ”

“ A disused and abandoned electric conductor, such as a telegraph
wire.
(c) A wire in use, but through which, at the time of speaking, no
current is passing.
Death, Electrical.
Death resulting from electricity discharged through the animal system.
The exact conditions requisite for fatal results have not been
determined. High electro-motive force is absolutely essential; a
changing current, pulsatory or alternating, is most fatal, possibly
because of the high electro-motive force of a portion of each period. ”

“ Just here we may refer to the fact—for it is a fact—that the electrical energy transmitted over a line, which may be many miles in length, really does not travel by the wire connecting the two points. It travels in the ether surrounding the wire. The wire itself is, in fact, the guiding core of the disturbances in the ether which proceed outward in all directions to unlimited distances. The guiding core or conducting wire is needed to focalize or direct the delivery of the energy. ”

“ It is evident that by merely depressing the handle till the upper lever comes in contact with the lower bar of metal at the point A, a current of electricity will flow through the point of contact from the battery wire to the telegraph wire. In order to break the contact or circuit, the operator has simply to desist from depressing the handle of the upper lever, which is instantly raised from contact by the action of the spring at the other end. ”

“ In the ordinary construction of transmission lines on land the tensile strength of wire is secondary in importance to its electrical conductivity, because supports can be spaced according to the strength of the conductor used. ”

“ A conducting body insulated from all other bodies will receive and hold a certain amount of electricity (a charge) , if subjected to an electrical potential. Thus, referring to Fig. 119, if a metal plate, insulated from other bodies, be connected with, say, the positive pole of a battery, the negative pole of which is grounded, a current will flow into the plate until the plate is raised to the same potential as that of the battery pole to which it is connected. ”

“ Now (if the power be sufficient) it does not signify what length of wire there may be between the two ends of this arrangement or “battery,” whether the ends be connected by a few feet of wire, or as many hundred miles—the electricity passes instantaneously from one end to the other; and furthermore, it has been found in practice, that this electrical influence can be transmitted through the earth in one direction if sent by a wire in the other; for instance, if a wire from one end of the battery be carried on from London to Liverpool ”

“ On turning the plate, a faint snapping sound is heard, and when the room is darkened, a spark is seen to be thrown out from the knob projecting from the prime conductors.
Many curious and interesting experiments may be performed by means of the machine, illustrating the general properties of electricity. For instance: a person standing on an insulated bench, that is, a bench with glass legs, or having the legs resting on glass, and having one hand on the conductor, can send sparks, with the other hand, to everything and everybody about. This illustrates communication of electricity by contact. ”

“ The annunciator has a bell to call attention. A cable of six wires enters this annunciator (Fig. 36) . One wire goes direct to the bell and the other five reach the bell through the separate coils of the electro-magnets which control the drops. But how are [70] electrical connections made between a moving elevator car and the push buttons on various floors? The diagram in Fig. 37 shows this in elevation. B represents a battery of several dry cells located in the basement. One wire from it runs direct to the push buttons 1, 2, 3, 4, 5, located upon the five floors of the house. ”

“ It is known since a long time that electric currents may be propagated through the earth, and this knowledge has been utilized in many ways in the transmission of signals and the operation of a variety of receiving devices remote from the source of energy, mainly with the object of dispensing with a return conducting-wire. ”

“ The facility with which alternating current can be transformed from one voltage to another, thus permitting high pressure transmission of electric energy to long distances through small wires, and low pressure distribution for the operation of lighting systems and motors, gives a far greater variety of systems of transmission and distribution than is possible with direct current. ”

“ Q shows a stout wire or strip of 2 or 3 thicknesses of tin. Suppose we have an apparatus, as, for example, an electric bell, which we want to have ring when someone at a distance desires to call us. If we use a telephone or telegraph instrument we shall want to cut the bell out of the circuit as soon as we hear the call and are ready to talk. Suppose the current comes to us through the wire, A, Fig. ”

“ In many electrical instruments a wire grating is used to prevent certain parts of the apparatus from being electrified by induction. We know that if a conductor be entirely surrounded by a metallic vessel at the same potential with itself, no electricity can be induced on the surface of the conductor by any electrified body outside the vessel. ”

“ It is very easy to detect the electric lines which radiate from every part of such a wire when a spark jumps between the terminals S of the coil. All that is necessary to do is to pass the wire through a sensitive film and to develop the film. The accompanying photograph (Fig. 3) was taken at the top of such a wire, by means of a very powerful apparatus at my command. When the photograph is examined with a microscope the arborescent electric lines radiating from the wire, like the rays of light Fig. 2a represents a more complete electrical arrangement of the receiver circuit. ”

“ The alternating current will operate incandescent lamps, arc lamps, electric heating apparatus, alternating current motors. It will flow through a straight wire with slightly increased retarding effect, but if the wire be wound on an iron bar its strength is greatly reduced. ”

“ Having described the electrical machine, we are now to consider some of the phenomena attending its operation. When the prime conductor receives electricity from the cylinder, it is said to be electrified by communication, and it then acts in every respect like the cylinder itself, except that the latter, when touched by a conductor communicating with the earth, gives a considerable number of sparks before it is discharged; whereas the conductor discharges itself by a single spark. ”

“ Fortunately for the future delivery of energy at great distances from its source, the means to avoid the limit just discussed are not difficult. Other experiments have shown that with a given voltage and distance between conductors the loss of energy from wire to wire decreases rapidly as their diameters increase. The electrical resistance of air, like that of any other substance, increases with the length of the circuit through it. The leakage described is a flow of electrical energy through the air from one wire to another of the same circuit. ”

“ Every one knows that when by means of an ordinary electrical machine electricity has been generated in sufficient quantity and under suitable conditions to prevent its dispersion, a spark of intense brilliancy and greater or less length, according to the amount of electricity thus collected, can be obtained when some body, not similarly electrified, is brought near to what is called the conductor of the machine. ”

“ A stout wire will transfer a bigger quantity in unit time than a thin wire, or, as we may also say, it is able to carry a bigger current. When it is a question of electricity in motion the conductor must have body, whilst as we have seen, with electricity at rest only the surface counts, or, to speak more correctly, only the capacity counts. ”

“ If an electrical oscillation is sent through this exceedingly fine platinum wire it heats it and rapidly increases its resistance. The electrical oscillations produced in an aerial are sent through a number of these loops arranged in parallel, and the loops are short-circuited by a telephone, joined in series with a source of very small electromotive force produced by shunting a single cell or opposing to one another two cells of nearly equal electromotive force. ”

“ Thus one lamp may be of relatively
double resistance compared to another, but this states nothing of the
resistance in ohms of either lamp.
Relay.
A receiving instrument which moves in accordance with impulses of
currents received, and in so moving opens and closes a local circuit,
which circuit may include as powerful a battery as required or
desirable, while the relay may be on the other hand so delicate as to
work with a very weak current.
Fig. 287. RELAY.
The typical relay includes an electro-magnet and armature. ”

“ So, instead of using a second wire, we use the earth to carry back the electricity to the battery, because the earth is a better conductor even than wire. Although a quantity of ground equal in size to the wire would offer thousands of times greater resistance than the wire, yet, owing to the great body [26] of our earth, its total resistance is even less than any telegraph wire used. ”

“ The object of a relay is generally to act as a sort of electrical multiplier, that is to say, it enables a comparatively weak current to bring into operation a much stronger current.
Fig. 2,276.—Diagram of connections of General Electric shunt trip coil with and without circuit opening auxiliary switch.
Ques. For what service are relays largely used?
Ans. They are employed in connection with high voltage switches where the small amount of energy derived from an ordinary instrument transformer is insufficient for tripping. ”

“ Electrical energy may be transmitted around the world if the line voltage is unlimited. This follows from the law that a given power may be transmitted to any distance with constant efficiency and a fixed weight of conductors, provided the voltage is increased directly with the distance.
The physical limits of electric-power transmission are thus fixed by the practicable voltage that may be employed. The effects of the voltage of transmission must be met in the apparatus at generating and receiving stations on the one hand, and along the line on the other. ”