Coil

“ We also sometimes meet with portions of the glass coil most ingeniously attached to and grouped with corals, shells and other marine products, which I need only refer to to remind you that such arrangements are entirely artificial, notwithstanding that they are often so artistically done as to have a most deceptively natural appearance, and that the way in which the coil is placed, with the free ends of the plume upward, has had, I imagine, considerable influence in persuading people that that was its ordinary mode of growth. ”

“ COIL-MADE WARE.
Coiling.—The art of building vessels by means of coils of clay has been practiced by many widely separated communities, and is, therefore, certainly not peculiar to the ancient Pueblos. A careful study of the ceramic field shows considerable diversity in the treatment of the coil. The most striking variation, the employment of the coil as a means of embellishment, is, so far as my observation extends, peculiar to the Pueblo peoples. With others it is a feature of construction simply. ”

“ Every one is familiar with the discharge of an ordinary coil; it need not be reproduced here. But, by way of contrast, here is a form of discharge of a coil, the primary current of which is vibrating several hundred thousand times per second. The discharge of an ordinary coil appears as a simple line or band of light. The discharge of this coil appears in the form of powerful brushes and luminous streams issuing from all points of the two straight wires attached to the terminals of the secondary. (Fig. 130.) ”

“ When the current through the primary is increased, the discharge gets broader and stronger, and the effect of the capacity of the coil becomes visible until, finally, under proper conditions, a white flaming arc, Fig. 100B, often as thick as one's finger, and striking across the whole coil, is produced. ”

“ A most curious form of discharge is observed with such a coil [Pg 219] when the frequency and potential are pushed to the extreme limit. To perform the experiment, every part of the coil should be heavily insulated, and only two small spheres—or, better still, two sharp-edged metal discs (d d, Fig. 140) of no more than a few centimetres in diameter—should be exposed to the air. The coil here used is immersed in oil, and the ends of the secondary reaching out of the oil are covered with an air-tight cover of hard rubber of great thickness. ”

“ When the potential is excessively high they will always appear, even if the frequency be low, and even if the primary be surrounded by as much as an inch of wax, hard rub [Pg 158] ber, glass, or any other insulating substance. This limits greatly the output of the coil, but I will later show how I have been able to overcome to a considerable extent this disadvantage in the ordinary coil. ”

“ If it is desired to construct a coil for the express purpose of performing with it such experiments as I have described, or, generally, rendering it capable of withstanding the greatest possible difference of potential, then a construction as indicated in Fig. 113 will be found of advantage. The coil in this case is formed of two independent parts which are wound oppositely, the connection between both being made near the primary. The potential in the middle being zero, there is not much tendency to jump to the primary and not much insulation is required. ”

“ If, however, we make the primary coil so that it can be slid in and out of the axis of the other, then while the primary current is continuously flowing, we can produce secondary currents in the other coil, by causing the coils to approach or recede from each other. ”

“ Fields due to Coils.—The most generally convenient arrangement for producing such magnetic fields as are required for experimental purposes is undoubtedly a coil of wire through which an electric current can be caused to flow. The field due to a coil can be made as nearly uniform as we please throughout a considerable space; its intensity, when the constants of the coil are known, can be calculated with ease and certainty and may be varied at will through wide ranges, while the apparatus required is of the simplest character and can be readily constructed to suit special purposes. ”

“ From this he now took a coil of wire—indeed, three small coils tied together—also a saucer of large dimensions of stone China, or thick, very thick porcelain, a large vial containing a colorless liquid, a box of paste or gum, two large, and entirely empty, thin bottles—so thin that we all looked through them at the light, as he handed them to us for that purpose. They were as clear as the best window glass, as thin and as brittle, apparently, as the finest crystal. ”

“ As the number of slots per coil-side is increased, an approach is gradually made to the case of “uniform distribution,” such as would obtain in a smooth-core armature in which the turns of the coil are wound closely side by side. Thus in the six-turn coil of fig. 12 A, which represents the development of a two-pole armature when the core is cut down to the shaft and opened out flat, there are in effect six phases compounded together, each of which differs but little from that of its next neighbour. ”

“ Primary Induction Coils.—These represent the simplest form of coil, and are used chiefly in low tension ignition to intensify the spark when a battery forms the current source.
A primary coil consists of a long iron core wound with a considerable length of low resistance insulated copper wire, the length of the core and the number of turns of the insulated wire winding determining the efficiency. The effect of the iron core is to increase the self-induction. ”

“ As we near the washing spot, in every direction immense hose, made of galvanized iron, and canvas tubes six feet round, coil in all directions over the ground like gigantic serpents, converging towards a gap, where they disappear. ”

“ Let be the area of the quadrilateral whose angles are the sections of the axes of four neighbouring wires of the coil by a plane through the axis, then is the volume occupied in the coil by a length of wire together with its insulating covering, and including- any vacant space necessarily left between the windings of the coil. Hence the whole volume of the coil is
,
(5) where is considered a function of . But since the coil is a figure of revolution
,
(6) or, expressing in terms of , by equation (2) ,
. ”

“ These coils should, however, be larger—about an inch wide and long enough to go all around the bowl once. Join every coil in the same way, taking care to press each one against the sides of the mould as well as upon the coil beneath, and to smooth the inside of the bowl with your fingers and the modelling tools. After attaching a coil, let the bowl dry for ten or fifteen minutes—in the air, unless it is a cold day. Be careful never to let your clay work freeze or it will be spoiled. When the bowl is about two inches and a half high set it away overnight to dry. ”

“ The space between the spring and over coil at the point where the over coil rises and curves over the spring should be at least equal to the width of the coils and care should be taken to see that the over coil just before the point of rising has the usual space between it and the next coil. Either position in which the hairspring may rub will have a shorter motion and a gain in time compared to the opposite position in which there is no interference. ”

“ When the space is filled up to the level of the paper disks and the paraffin is hard, loosen the set screw, and removing the outside disk, the coil can be slipped off, or a slight warming will loosen it. Any number of these coils can be made, and there are the advantages in this mode of construction that a bad coil will not spoil the whole secondary, and that the wire can be obtained in comparatively small quantities. ”

“ When applied to coils, the two fibres are no longer of silk but of metal, and since the torsion of a metal wire capable of supporting the coil and transmitting the current is much greater than that of a silk fibre, it must be taken specially into account. ”

“ But these writers had paid too little attention to classical writers like La Grange, Thomson, and Kirchhoff. The construction of the inductance-coil required almost as much mathematical analysis as the dynamical theory of the invention, and the method of testing it also was new to the telephone engineers. The coil is now known all over the world as the Pupin coil, and many people think that the coil itself is the invention. ”

“ The principle of the circulation of the particles of water being once understood, it is easy to comprehend how it is applied to the heating of buildings by what is called the "Hot Water Apparatus." A coil of pipe is enclosed in a proper furnace, and the bottom end communicates with a pipe coming from a second tube or set of coils, placed above it in another apartment, whilst the top of the latter coil communicates with the top pipe of the first coil. ”

“ A tuner of this kind is made like an ordinary loose coupled tuning coil but it has a third coil as shown at A and B in Fig. 49. The middle coil, which is the secondary, is fixed to the base, and the large outside coil, which is the primary, is movable, that is it slides to and fro over the middle coil, while the small inside coil, which is the tickler, is also movable and can slide in or out of the middle coil. None of these coils is variable; all are wound to receive waves up to 360 meters in length when used with a variable condenser of .001 mfd. capacitance. ”

“ II. When the deflecting force acts at right angles always to the
controlling force.
These conditions are usually secured by having the actuating coil
through which the current passes flat and of large diameter compared to
the length of the needle; by using the uniform field of the earth as the
control; by having a short needle; by placing the coil with its plane in
the magnetic meridian.
For best proportions of tangent galvanometer coils see Bobbins.
Fig. 310. GRAPHIC CONSTRUCTION OF TANGENT SCALE.
Tangent Scale. ”

“ This new field of experiment has brought many into personal contact with coils who have never had any acquaintance with such instruments before, and it is thought that some will like to have a convenient outline of the many other impressive and beautiful experiments in which the induction coil bears a part. ”

“ For current indicators, a pivoted or suspended copper band or ring composed of thin washers piled together and insulated from one another, and made to carry a pointer or index has been placed in the axis of a coil conveying alternating currents whose amount or potential is to be indicated. Gravity or a spring is used to bring the index to the zero of a divided scale, at which time the plane of the copper ring or band makes an angle of, say, 15 degrees to 20 degrees with the plane of the coil. ”

“ If we wish to suspend a coil between two coils placed so near it that the distance between the mutually acting wires is small compared with the radius of the coils, the most uniform force is obtained by making the radius of either of the outer coils exceed that of the middle one by of the distance between the planes of the middle and outer coils. ”

“ It is, of course, absolutely necessary to employ in such a coil wires provided with the best insulation. Good coils may be produced by employing wires covered with several layers of cotton, boiling the coil a long time in pure wax, and cooling under moderate pressure. The advantage of such a coil is that it can be easily handled, but it cannot probably give as satisfactory results as a coil immersed in pure oil. ”

“ Given two coils at right angles and with their split-rings displaced through a corresponding angle of 90°, they may be connected in series by joining one brush to the opposite brush of the second coil, the external circuit being applied to the two remaining brushes.14 The same arrangement may again be repeated with another pair of coils in parallel with the first, and we thus obtain fig. ”

“ The intensely disruptive power of the long spark is readily shown by its power to perforate substances, but great care must be taken that the secondary wires of a coil are led away from the body of the coil. A good plan is to hang two silk cords or stout threads from the ceiling, to which the secondary wires may be attached and kept in sight when experimenting at any distance from the coil. ”

“ A half coil or hemitropic winding is one in which the coils in any phase are situated opposite every other pole, that is, a winding in which there is only one coil per phase per pair of poles, as in fig. ”

“ This experiment is analogous to the one illustrated by diagram 6, which represents the result of an experiment made to ascertain the relative strength of capability or producing inductive effects of different parts of a straight electro-magnet.
A, Fig. 1, represents the iron core, PP the primary coil, connected at pleasure to one Grove cell, B, by means of the key, K; S, a small secondary coil free to move along the primary coil while in circuit with the galvanometer, G. The relative strength of any particular spot can be obtained by moving the coil, S, exactly over the required position. ”

“ A wooden wedge driven into a groove at the top of each slot is often used to lock the coil in place. With slots nearly closed at the top, the coils are formed by hand by threading the wire through tubes of micanite or specially prepared paper lining the slots; or with single-turn loops, stout bars of copper of U-shape can be driven through the slots and closed by soldered connexions at the other end. ”

“ By a proper arrangement of several coils the field of force within them may be made much more uniform than when one coil only is used, and the dimensions of the instrument may be thus reduced and its sensibility increased. ”