Brush (electric)

“ However, with incomparably higher frequencies, which we may yet find means to produce efficiently, and provided that electric impulses of such high frequencies could be transmitted through a conductor, the electrical characteristics of the brush discharge would completely vanish—no spark would pass, no shock would be felt—yet we would still have to deal with an electric phenomenon, but in the broad, modern interpretation of the word. ”

“ H is a commutator of ordinary construction. When the electro-motive force between the brushes a and b, as the resistance of the circuit a, M, c-1, c, A, to the resistance of the circuit b, B, c, c-1, D, the potentials of the points x and y, will be equal and no current will pass over the auxiliary brush c, but if said brush occupies a different position relatively to the main brushes, the electric condition is disturbed and current will flow either from y to x, or from x to y, according to the relative position of the brushes. ”

“ By adjusting this contact, which is movable, the electric oscillations created in the short section of the resonator coil produce by resonance oscillations in the longer free section, and a powerful high frequency electric brush or discharge is produced at the free end of the resonator spiral. An electrode or wire connected with this free end therefore furnishes a high frequency glow discharge which has been found to have valuable therapeutic powers. ”

“ The discharge by a brush is not to all the particles of air that are near the electrified conductor from which the brush issues; only those parts where the ramifications pass are electrified: the air in the central dark parts between them receives no charge, and, in fact, at the time of discharge, has its electric and inductive tension considerably lowered. For consider fig. ”

“ This is effected by shifting them until sparking between them and the
commutator is nearly or quite suppressed.
Fig. 68. BRUSH HOLDER.
Brushes, Lead of.
In a dynamo electric generator, the lead or displacement in advance of
or beyond the position at right angles to the line connecting the poles
of the field magnet, which is given the brushes. In a motor the brushes
are set back of the right angle position, or are given a negative lead.
(See Lag.)
91 STANDARD ELECTRICAL DICTIONARY.
Brush Holders. ”

“ There is a crackling electric tension in the air—then acheer, and a general surge toward the platform's edge. The locomotive blows its warm quick breath against their faces, crashes past, stops. Strings of girls begin to spill from every coach. ”

“ He lay late abed every morning, and took a combination breakfast and lunch with Yvonne, either at her apartment, where they made electric coffee and electric toast and chafing-dish scrambled eggs, or at his own apartment, where the ubiquitous Bennett served them, Then they sallied forth. Sometimes to a matinee. Sometimes to a vaudeville show, for business reasons. Sometimes to buy new ragtime selections at a little Broadway shop, and take them back and try them out together. Sometimes, if the day was hot, to scoot into the country in the roadster, or to swim at some not too populous beach. ”

“ The brush form of disruptive discharge may be obtained not only in air and gases, but also in much denser media. I procured it in oil of turpentine from the end of a wire going through a glass tube into the fluid contained in a metal vessel. The brush was small and very difficult to obtain; the ramifications were simple, and stretched out from each other, diverging very much. The light was exceedingly feeble, a perfectly dark room being required for its observation. When a few solid particles, as of dust or silk, were in the liquid, the brush was produced with much greater facility. ”

“ Sometimes a brush may be formed of only six or seven branches, these being broad and highly luminous, of a purple colour, and in some parts an inch or more apart: by a spark discharge at the prime conductor (1455.) single brushes may be obtained at pleasure. Discharge in the form of a brush is favoured by rarefaction of the air, in the same manner and for the same reason as discharge in the form of a spark (1375.) ; but in every case there is previous induction and charge through the dielectric, and polarity of its particles (1437.) ”

“ At least two brushes per ring are always provided so that one can be removed for inspection without interrupting the exciting current. In large machines the brush holder studs are mounted on a stand supported from the base ”

“ It is usual, except in the smallest machines, to place at least two brushes exactly similar side by side instead of one broad brush, thus allowing one brush to be removed for trimming or renewal while the machine is running. Moreover, better contact is secured by this sub-division, because a slight elevation in the commutator surface at one point may slightly raise one brush of a set at each revolution without much harm, while with one broad brush, the entire brush would be lifted, causing bad sparking. ”

“ If the rounded end of a metal rod, 0.15 of an inch in diameter, be made to give a good negative brush, the approach of a smaller end or a blunt point opposite to it will, at a certain distance, cause a diminution of the brush, and a glow will appear on the positive inducteous wire, accompanied by a current of air passing from it. Now, as the air is being charged both at the positive and negative surfaces, it seems a reasonable conclusion, that the charged portions meet somewhere in the interval, and there discharge to each other, without producing any luminous phenomena. ”

“ Tension on the brush head is obtained by a special spring which maintains any given tension for which it may be set. An auxiliary flat steel spring on the lower side of the lever acts as a shock absorber between the lever and the brush head, absorbing all minor vibrations caused by a worn commutator. Side contact between brush and brush holder is not relied upon to carry the current, flexible copper pigtails performing this function to the exclusion of sliding contacts or tension springs, in order to reduce the brush loss. ”

“ Indeed, we find that the brush is hot, and only a little thought leads us to the conclusion that, could we but reach sufficiently high frequencies, we could produce a brush which would give intense light and heat, and which would resemble in every particular an ordinary flame, save, perhaps, that both phenomena might not be due to the same agent—save, perhaps, that chemical affinity might not be electrical in its nature. ”

“ Frictional Electricity is that produced by the friction of one substance against another.
Resinous Electricity.—The kind of electricity produced upon a resinous substances such as sealing wax, resin, shellac, rubber or amber when rubbed with wool or fur. Resinous electricity is negative electricity.
Vitreous Electricity.—A term applied to the positive electricity developed in a glass rod by rubbing it with silk. This electric charge will attract to itself bits of pith or paper which have been repelled from a rod of sealing wax or other resinous substance which had been rubbed with wool or fur. ”

“ I have dwelt at some length upon the various forms of brush discharge because, in studying them, we not only observe phenomena which please our eye, but also afford us food for thought, and lead us to conclusions of practical importance. In the use of alternating currents of very high tension, too much precaution cannot be taken to prevent the brush discharge. In a main conveying such currents, in an induction coil or transformer, or in a condenser, the brush discharge is a source of great danger to the insulation. ”

“ Fig. 701.--Test for break in armature lead. Clean the brushes and commutator, and apply current from a few cells of battery having a telephone receiver in circuit as shown in the figure. If the machine have more than two brushes, connect the leads to two adjoining brushes and raise the others. Now rotate the armature slowly by hand and there will be a distinct click in the receiver as each segment passes under the brushes until one brush bears on the segment at fault, when the clicking will cease. In making this test, the brushes must not cover more than a single segment. ”

“ 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. ”

“ Greasing the end of a rounded wire will immediately make it produce brushes instead of glow. A ball having a blunt point which can be made to project more or less beyond its surface, at pleasure, can be made to produce every gradation from glow, through brush, to spark. ”

“ The brush and spark gradually pass into one another, Making a small ball positive by a good electrical machine with a large prime conductor, and approaching a large uninsulated discharging ball towards it, very beautiful variations from the spark to the brush may be obtained. ”

“ It is, therefore, evident that, when a ball is discharging electricity in the form of brushes, the brushes are far more numerous, and each contains or carries off far less electric force when the electricity so discharged is negative, than when it is positive. ”

“ This is done merely to enable the apparatus to perform the work which it is not capable of performing at ordinary air pressure. In the bulb we are able to intensify the action to any degree—so far that the brush emits a powerful light. ”

“ All substances that conduct electricity resist the flow somewhat; there is something like friction between the wire and the electricity passing through it. The smaller around a wire is, the greater resistance it offers to the passing of an electric current. The filament of an electric lamp is very fine and therefore offers considerable resistance. However, if the filament were made of copper, even as fine as it is, it would take a much greater flow of electricity to make it white hot, and it would be very expensive to use. ”

“ A series of rapid and successive reunions of the electricity with each bristle of the brush takes place, generating a current of cold air perceptible to the patient. I habitually use for this application an ordinary clothes-brush. If while in connection with the conductor any object (the knuckles will do) is brought sufficiently near to the patient for his contained electricity to overcome the resistance of the intervening stratum of air, he is “discharged” with a spark. This is Franklinization by sparks, and is accompanied by a certain slight amount of “shock.” ”

“ Fig 323.—Showing how a Glass-Plate Condenser is built up of Alternate Sheets of Tinfoil and Glass. The weird beauty of a Tesla coil is only evident when it is operated in the dark. The two wires leading from the secondary to the brass rods and the ball on the ends of the rods will give forth a peculiar brush discharge.
If you take a piece of metal in your hand and hold it near one of the secondary terminals, the brushing will increase. If you hold your hand near enough, a spark will jump on to the metal and into your body without your feeling the slightest sensation. ”

“ In all such experiments as those described, the point of change from spark to brush is very much governed by the working state of the electrical machine and the size of the conductor connected with the discharging ball. If the machine be in strong action and the conductor large, so that much power is accumulated quickly for each discharge, then the interval is greater at which the sparks are replaced by brushes ”

“ These things being premised, the phenomena of charging and discharging a plate of glass, or a Leyden phial, may be easily solved. In the usual manner of electrifying by a smooth glass globe or cylinder, all the electric matter is supplied by the rubber, from all the bodies which communicate with it. ”

“ In the positive brush of a static machine the exchange of the molecules is very rapid, the stream is constantly of one direction, and there are fewer collisions; hence the heating effect must be very small. Anything that impairs the facility of exchange tends to increase the local heat produced. Thus, if a bulb be held over the terminal of the coil so as to enclose the brush, the air contained in the bulb is very quickly brought to a high temperature. If a glass tube be held over the brush so as to allow the draught to carry the brush upwards, scorching hot air escapes at the top of the tube. ”

“ When the brush discharge is observed in air at the positive and negative surfaces, there is a very remarkable difference, the true and full comprehension of which would, no doubt, be of the utmost importance to the physics of electricity ”

“ We may by this means accumulate a vast quantity of opposite electricities on the two coatings of such a jar, and they will remain there for a long time, especially if the surrounding atmosphere and the glass surface of the jar be quite dry. When, however, electric connection of any kind is made between the two coatings, the electricities rush together and unite with one another in the shape of a spark, while if the human body be the instrument of connecting them a severe shock will be felt. ”