The Inventions, Researches and Writings of Nikola Tesla

sustained upon[Pg 458] any suitable support. They are shown as connected with the upper end of the core of the magnet N. Around the carbon-holding rod S, between the plates S' S2, there is a tube, R, which forms a clamp. This tube is counter-bored, as seen in the section Fig. 282, so that it bears upon the rod S at its upper end and near the middle, and at the lower end of this tubular clamp R there are armature segments r of soft iron. A frame or arm, n, extending, preferably, from the core N2, supports the lever A by a fulcrum-pin, o. This lever A has a hole, through which the upper end of the tubular clamp R passes freely, and from the lever A is a link, q, to the lever t, which lever is pivoted at y to a ring upon one of the columns S3. This lever t has an opening or bow surrounding the tubular clamp R, and there are pins or pivotal connections w between the lever t and this clamp R, and a spring, r2, serves to support or suspend the weight of the parts and balance them, or nearly so. This spring is adjustable. At one end of the lever A is a soft-iron armature block, a, over the core M' of the helix M, and there is a limiting screw, c, passing through this armature block a, and at the other end of the lever A is a soft iron armature block, b, with the end tapering or wedge shaped, and the same comes close to and in line with the lateral projection e on the core N2. The lower ends of the cores M' N2 are made with laterally projecting pole-pieces M3 N3, respectively, and these pole-pieces are concave at their outer ends, and are at opposite sides of the armature segments r at the lower end of the tubular clamp R. The operation of these devices is as follows: In the condition of inaction, the upper carbon rests upon the lower one, and when the electric current is turned on it passes freely, by the frame and spring l, through the rods and carbons to the coarse wire and helix M, and to the negative binding post V and the core M' thereby is energized. The pole piece M3 attracts the armature r, and by the lateral pressure causes the clamp R to grasp the rod S', and the lever A is simultaneously moved from the position shown by dotted lines, Fig. 278, to the normal position shown in full lines, and in so doing the link q and lever t are raised, lifting the clamp R and S, separating the carbons and forming the arc. The magnetism of the pole piece e tends to hold the lever A level, or nearly so, the core N2 being energized by the current in the shunt which contains the helix N. In this position the lever A is not[Pg 459] moved by any ordinary variation in the current, because the armature b is strongly attracted by the magnetism of e, and these parts are close to each other, and the magnetism of e acts at right angles to the magnetism of the core M'. If, now, the arc becomes too long, the current through the helix M is lessened, and the magnetism of the core N3 is increased by the greater current passing through the shunt, and this core N3, attracting the segmental armature r, lessens the hold of the clamp R upon the rod S, allowing the latter to slide and lessen the length of the arc, which instantly restores the magnetic equilibrium and causes the clamp R to hold the rod S. If it happens that the carbons fall into contact, then the magnetism of N2 is lessened so much that the attraction of the magnet M will be sufficient to move the armature a and lever A so that the armature b passes above the normal position, so as to separate the carbons instantly; but when the carbons burn away, a greater amount of current will pass through the shunt until the attraction of the core N2 will overcome the attraction of the core M' and bring the armature lever A again into the normal horizontal position, and this occurs before the feed can take place. The segmental armature pieces r are shown as nearly semicircular. They are square or of any other desired shape, the ends of the pole pieces M3, N3 being made to correspond in shape. In a modification of this lamp, Mr. Tesla provided means for automatically withdrawing a lamp from the circuit, or cutting it out when, from a failure of the feed, the arc reached an abnormal length; and also means for automatically reinserting such lamp in the circuit when the rod drops and the carbons come into contact. Fig. 283 is an elevation of the lamp with the case in section. Fig. 284 is a sectional plan at the line x x. Fig. 285 is an elevation, partly in section, of the lamp at right angles to Fig. 283. Fig. 286 is a sectional plan at the line y y of Fig. 283. Fig. 287 is a section of the clamp in about full size. Fig. 288 is a detached section illustrating the connection of the spring to the lever that carries the pivots of the clamp, and Fig. 289 is a diagram showing the circuit-connections of the lamp. In Fig. 283, M represents the main and N the shunt magnet, both securely fastened to the base A, which with its side columns, S S, are cast in one piece of brass or other diamagnetic material. To the magnets are soldered or otherwise fastened the brass washers or discs a a a a. Similar washers, b b, of fibre or other insu[Pg 460]lating material, serve to insulate the wires from the brass washers. The magnets M and N are made very flat, so that their width exceeds three times their thickness, or even more. In this way a comparatively small number of convolutions is sufficient to produce the required magnetism, while a greater surface is offered for cooling off the wires. Fig. 286.Fig. 283. Fig. 285. Fig. 287.Fig. 288. Fig. 284. The upper pole pieces, m n, of the magnets are curved, as indicated in the drawings, Fig. 283. The lower pole pieces m' n', are brought near together, tapering toward the armature g, as shown in Figs. 284 and 286. The object of this taper is to concentrate the greatest amount of the developed magnetism upon the armature, and also to allow the pull to be exerted always upon the middle of the armature g. This armature g is a piece of iron[Pg 461] in the shape of a hollow cylinder, having on each side a segment cut away, the width of which is equal to the width of the pole pieces m' n'. The armature is soldered or otherwise fastened to the clamp r, which is formed of a brass tube, provided with gripping-jaws e e, Fig. 287. These jaws are arcs of a circle of the diameter of the rod R, and are made of hardened German silver. The guides f f, through which the carbon-holding rod R slides, are made of the same material. This has the advantage of reducing greatly the wear and corrosion of the parts coming in frictional contact with the rod, which frequently causes trouble. The jaws e e are fastened to the inside of the tube r, so that one is a little lower than the other. The object of this is to provide a greater opening for the passage of the rod when the same is released by the clamp. The clamp r is supported on bearings w w, Figs. 283, 285 and 287, which are just in the middle between the jaws e e. The bearings w w are carried by a lever, t, one end of which rests upon an adjustable support, q, of the side columns, S, the other end being connected by means of the link e' to the armature-lever L. The armature-lever L is a flat piece of iron in N shape, having its ends curved so as to correspond to the form of the upper pole-pieces of the magnets M and N. It is hung upon the pivots v v, Fig. 284, which are in the jaw x of the top plate B. This plate B, with the jaw, is cast in one piece and screwed to the side columns, S S, that extend up from the base A. To partly balance the overweight of the moving parts, a spring, s', Figs. 284 and 288, is fastened to the top plate, B, and hooked to the lever t. The hook o is toward one side of the lever or bent a little sidewise, as seen in Fig. 288. By this means a slight tendency is given to swing the armature toward the pole-piece m' of the main magnet. The binding-posts K K' are screwed to the base A. A manual switch, for short-circuiting the lamp when the carbons are renewed, is also fastened to the base. This switch is of ordinary character, and is not shown in the drawings. The rod R is electrically connected to the lamp-frame by means of a flexible conductor or otherwise. The lamp-case receives a removable cover, s2, to inclose the parts. The electrical connections are as indicated diagrammatically in Fig. 289. The wire in the main magnet consists of two parts, x' and p'. These two parts may be in two separated coils or in[Pg 462] one single helix, as shown in the drawings. The part x' being normally in circuit, is, with the fine wire upon the shunt-magnet, wound and traversed by the current in the same direction, so as to tend to produce similar poles, N N or S S, on the corresponding pole-pieces of the magnets M and N. The part p' is only in circuit when the lamp is cut out, and then the current being in the opposite direction produces in the main magnet, magnetism of the opposite polarity. The operation is as follows: At the start the carbons are to be in contact, and the current passes from the positive binding-post K to the lamp-frame, carbon-holder, upper and lower carbon, insulated return-wire in one of the side rods, and from there through the part x' of the wire on the main magnet to the negative binding-post. Upon the passage of the current the main magnet is energized and attracts the clamping-armature g, swinging the clamp and gripping the rod by means of the gripping jaws e e. At the same time the armature lever L is pulled down and the carbons are separated. In pulling down the armature lever L the main magnet is assisted by the shunt-magnet N, the latter being magnetized by magnetic induction from the magnet M. Fig. 289. It will be seen that the armatures L and g are practically the keepers for the magnets M and N, and owing to this fact both magnets with either one of the armatures L and g may be considered as one horseshoe magnet, which we might term a "compound magnet." The whole of the soft-iron parts M, m', g, n', N and L form a compound magnet.[Pg 463] The carbons being separated, the fine wire receives a portion of the current. Now, the magnetic induction from the magnet M is such as to produce opposite poles on the corresponding ends of the magnet N; but the current traversing the helices tends to produce similar poles on the corresponding ends of both magnets, and therefore as soon as the fine wire is traversed by sufficient current the magnetism of the whole compound magnet is diminished. With regard to the armature g and the operation of the lamp, the pole m' may be considered as the "clamping" and the pole n' as the "releasing" pole. As the carbons burn away, the fine wire receives more current and the magnetism diminishes in proportion. This causes the armature lever L to swing and the armature g to descend