Electrical apparatus

“ 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. ”

“ 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. ”

“ A.D. 1772.—Henley (William T.) , F.R.S., invents the quadrant electrometer, an apparatus with which the quantity of electricity accumulated in a jar or battery can be measured through the amount of repulsion produced by the fluid upon a pith ball suspended from the centre of a graduated arc. It is generally attached to the prime conductor to measure the state of action of the electrical machine. ”

“ 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. ”

“ 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. ”

“ After demonstrating the practicability of this method of transmission, the thought naturally occurred to me to use the earth as a conductor, thus dispensing with all wires. Whatever electricity may be, it is a fact that it behaves like an incompressible fluid, and the earth may be looked upon as an immense reservoir of electricity, which, I thought, could be disturbed effectively by a properly designed electrical machine. Accordingly, my next efforts were directed toward perfecting a special apparatus which would be highly effective in creating a disturbance of electricity in the earth. ”

“ However extraordinary the results shown may appear, they are but trifling compared with those which are attainable by apparatus designed on these same principles. I have produced electrical discharges the actual path of which, from end to end, was probably more than one hundred feet long; but it would not be difficult to reach lengths one hundred times as great. I have produced electrical movements occurring at the rate of approximately one hundred thousand horse-power, but rates of one, five, or ten million horse-power are easily practicable. ”

“ Before entering into the description of the electrotype, we must say a few words on the subject of electricity to the less informed of our readers. The electric fluid, as it is called, may be produced in various ways: the most ordinary is by the friction of glass against silk, as exemplified in the electrical machine, which is familiar to almost every one. But galvanic and voltaic electricity is differently produced. ”

“ 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. ”

“ 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. ”

“ Electricians now began to be sedulous in their experiments upon the new force by friction, then the only known method of generating electricity. In 1729, Stephen Gray, a pensioner of the Charter-house, contrived a method of making electrical signals through a wire 765 feet long ”

“ It is not our purpose here to describe at length the electrical machine, but we may state that it consists of two parts, one for generating electricity by means of the friction of a rubber against glass, and another consisting of a system of brass tubes, of considerable surface, supported on glass stems, for collecting and retaining the electricity so produced. This latter part of the machine is called its prime conductor. ”

“ 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. ”

“ The electrical machines in common use are composed of a hollow glass cylinder, or circular plate of glass, turning on an axis, and rubbing against two or more leather rubbers covered with silk, the electricity being collected by sharp points fixed in a metal rod standing on a glass pillar. ”

“ The watt or practical unit of work (or rather, the rate of doing work) is equal to 10,000,000 ergs per second, or to the work produced in one second by one ampere of current of an E. M. F. of one volt, acting through the resistance of one ohm.
The practical electrical units are called after the eminent scientific investigators whose names they bear.
BATTERIES. The portion of the copper plate (or carbon) from which the current flows through the wire is called the positive pole (sometimes anode) , and the zinc plate the negative pole (sometimes cathode) . ”

“ In the case, therefore, of the electrical machine, it appears that the accumulation of electricity in an insulated conductor is always accompanied by the excitement of the contrary electricity in the surrounding atmosphere, and in every conductor placed near the former conductor. It does not seem possible, in this case, to produce one electricity by itself. ”

“ The Sounder is a simpler instrument than the Recorder, and is in more general use. The chief part of its operation is effected by means of the relay or local battery. A simple illustration shows its essential parts. When a current of electricity from the transmitter comes along the telegraph wire, it enters the electro-magnet E M, which forms the central part of the apparatus, and which, being thus electrified, attracts to itself the armature C, just above it. ”

“ 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. ”

“ Faraday's term “electrode,” literally a way for electricity to travel along, might be well applied to designate the insulated conductor along which the electric messenger is despatched. It is, how ever, more commonly and familiarly called “the wire” or “the line.”
The apparatus for generating the electric action at one end is commonly called the transmitting apparatus or instrument, or the sending apparatus or instrument, or sometimes simply the transmitter or sender. ”

“ Replace it, and let the cylinder be again wiped; the machine is fit for use.
4. Sometimes the electric matter will not be well collected, because the machine is not sufficiently supplied with it from the earth; which happens, when the table upon which the electrical machine is placed and to which the chain or wire of the rubber is connected, is very dry, and consequently a bad conductor. In this case, the best method is to connect the chain or wire of the rubber with some moist ground, or with the iron-work of a water-pump, if convenient. ”

“ In use either the prime conductor or cushions are connected by a chain
or otherwise with the earth. Assume it to be the cushions. As the
machine is worked by turning the plate, the glass and cushion being in
contact develop opposite electricities. The glass is charged with
positive electricity, and as it turns carries it off and as it reaches
the prime conductor by induction and conduction robs it of its negative
electricity. Meanwhile the cushions negatively excited deliver their
charge to the earth. The action thus goes on, the prime conductor being
charged with positive electricity. ”

“ If the electrical stand be kept clean and dry, a man standing on it when such clouds are passing low, might be electrified and afford sparks, the rod drawing fire to him from a cloud. If any danger to the man should be apprehended (though I think there would be none) let him stand on the floor of his box, and now and then bring near to the rod, the loop of a wire that has one end fastened to the leads, he holding it by a wax handle; so the sparks, if the rod is electrified, will strike from the rod to the wire, and not affect him. ”

“ 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. ”

“ Now, if you grasp the outside of the coated end with one hand, and touch the knobbed wire with the other, you will receive a shock.
96In this experiment, the coated part of the tube answers the double purpose of the electrical machine and Leyden phial; the uncoated part serving as a handle, to hold the instrument by. The friction on the outside accumulates a quantity of positive electricity upon it, and this electricity, in virtue of its sphere of action, forces out a quantity from the inside. ”

“ CONDUCTORS AND INSULATORS
Bodies differ from each other in a striking manner in the freedom with which the electric current moves upon them. If the electric current be imparted to a certain portion of the surface of glass or wax, it will be confined strictly to that portion of the surface which originally receives it, by contact with the source of electricity ”

“ If an insulated conductor, connected with the positive conductor of an electrical machine, have a metal rod 0.3 of an inch in diameter projecting from it outwards from the machine, and terminating by a rounded end or a small ball, it will generally give good brushes; or, if the machine be not in good action, then many ways of assisting the formation of the brush can be resorted to ”

“ Next to the mechanism by which electric signals are made intelligible, one of the most important inventions is that by which an electric current is enabled to renew its strength as it goes along a great length of wire. The apparatus used for this purpose is called a relay, and the first man to publish an account of it was Prof. Wheatstone. Its mechanism is delicate and sometimes complex, but its principle can be easily understood. ”

“ 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. ”

“ All wires and current carrying parts should be kept far enough apart at all points to prevent accidental contact or the jumping across of the 428 current where there is a great difference of voltage. Such wires should be also kept at a sufficient distance from screw heads, metal brackets, gas pipes, water pipes, and other conducting bodies, in order to prevent accidental grounds or short circuits. ”

“ 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. ”

“ Non-electric Bodies made electrical, lose almost all that Electricity by coming either within 5 or near the Contact of Non-electrics not made electrical; it happens otherwise with Regard to Electrics per se, when excited by rubbing, patting, &c; because from the rubbed Tube I can sometimes procure five or six Flashes from different Parts, as though the Tube of two Foot long, instead of being one continued Cylinder, consisted of five or six separate Segments of Cylinders, each of which gave out its Electricity at a different Explosion. ”