Chapter XII: TECHNOLOGY.--Notes on Dyewood Extracts and Similar (2)

The uneven distribution of current, or its tendency to flow on the outer parts of a conductor when the rate of variation or alternation is made great, is in itself a consequence of the fact that less energy is transferred into magnetism in this case than when the current flows uniformly over the section, or is concentrated at the center. In other words, when a uniform current traverses a conductor of the same section, the circular magnetism, or surrounding magnetic lines, are to be found not only outside the conductor, but also beneath its exterior. Since in forming these lines on passage of current the middle of section would be surrounded by more lines than any other part of the conductor, the current tends to keep out of that part and move nearer the exterior in greater amount. Hence, in rapidly alternating currents the conductor section is practically lessened, being restricted largely to the outer metal of the conductor. If the round conductor, Fig. 2, were made of iron, the magnetism interior to it and set up by a current in it would be very much greater, the section of the conductor being filled with magnetic circuits or lines around the center. The total magnetism, external and internal, would be much greater in this case for a given current flow, and the energy absorbed and given out in formation and loss of field or the self-induction would be much increased. This could, however, be greatly diminished by slitting the conductor radially or making it of a number of separate wires out of lateral magnetic contact one with the other, Fig. 3. In these cases the resistance of the interior magnetic circuits would be increased, as there would be several breaks in the continuity around the center of the conductor. The total magnetism which could be set up by a current would be lessened, and the self-induction, therefore, lessened.

The moment we begin the bringing of iron into proximity with an electric conductor conveying current, we provide a better medium for the flow or development of magnetic lines or circuits. In other words, the lines may then be longer, yet equally intense, or more lines may be crowded into a section of this metal than in air or space. Figs. 4a, 4b, 4c show the effect brought about by bringing iron of different forms near to the conductor.

It shows, in other words, the development of the ordinary electro-magnet of the horseshoe form, and the concentration of the lines in the better medium. The lines also tend to shorten and diminish the resistance to their passage, so that attraction of the iron to the conductor takes place, and if there is more than one piece of iron, they tend to string themselves around the conductor in magnetic contact with one another.

When copper bars of 1 inch diameter are traversed by currents of 40,000 to 60,000 amperes, as in welding them, the magnetic forces just referred to become so enormous that very heavy masses of iron brought up to the bar are firmly held, even though the current be of an alternating character, changing direction many times a second.

When a conductor is surrounded by a cast iron ring, as in Fig. 5, the current in such conductor has an excellent magnetic medium surrounding it. A large amount of energy is then abstracted on the first impulse of current, which goes to develop strong and dense magnetic lines through the iron ring and across the gap in it. On taking off the current the energy is returned as extra current, and its force is many times what would be found with air alone surrounding the conductor. We have then greatly increased the self-induction, the storing of energy and opposition to current flow at the beginning, the giving back of energy and assistance to the current flow on attempting to remove or stop the current. Let us now complete the ring, by making it of iron, endless, Fig. 6, with the conductor in the middle.

We now find that on passing current through the conductor it meets with a very strong opposing effect or counter potential. The evolution of magnetic lines, or the opening out of magnetic circuits, goes on at a very rapid rate. Each line or magnetic circuit evolved, and cutting the conductor, flies at once outward, and locates itself in the iron ring. This ring can carry innumerable lines, and they do not crowd one another. It permits the lines even to lengthen in reaching it, and yet, on account of its low resistance to their passage, the lengthening is equivalent to their having shortened in other media. We will suppose the current not sufficient to exhaust this peculiar capacity for lines which the iron has. Equilibrium is reached, the conductor has opened up innumerable closed circuits, and caused them to exist in the ring still closed; but in iron, not space or ether merely. The current passing has continued its action and storage of energy until to emit another line in view of the resistance now found in the crowded iron ring is impossible.

Now let us cut off the current. We are surprised to find a very weak extra current, a practical absence of self-induction on breaking, or, at least, a giving out of energy in nowise comparable to that on making. Let us put on the current as it was before. Another curious result. But little self-induction now on making energy not absorbed.

Now cut off the current again. Same effect as before. Now let us put on the current reversed in direction. At once we find a very strong counter potential or opposing self-induction developed.

The ring had been polarized, or retained its magnetic energy, and we are now taking out one set of lines and putting in reversely polarized lines of force. This done, we break the reversed current without much effect of self-induction. The ring remains polarized and inert until an opposite flow of current be sent through. Iron is then a different medium from the ether.

The ring once magnetized must, in losing its magnetism, permit a closure of the lines by shortening. This involves their passage from the iron across the space in the center of the ring, notwithstanding its great resistance to the lines of force. As passage from iron to air is equivalent to lengthening of the lines, it is readily seen that such lengthening may oppose more effect than a slight shortening due to leaving iron, for air or space may give in provoking a closure and disappearance of the lines. Looked at from another standpoint, the lines on the iron may actually require a small amount of initial energy to dislodge them therefrom, so that after being dislodged they may collapse and yield whatever energy they represent.

I must reserve for the future further consideration of the iron ring, but in thinking upon this matter I am led to think that the production of a magnetic line in an iron ring around a conductor may represent a sort of wave of energy, an absorption of energy on the evolution of the line from the conductor, and a slight giving out of energy on the line reaching that position of proximity to the iron ring, that its passage thereto may be said to be a shortening process or a lessening of its resistance.

The magnetism in air, gases, and non-magnetic bodies, being assumed to be that of the ether, this medium shows no such effects as those we get with the ring. It does not become permanently polarized, as does even soft iron under the condition of a closed ring. The iron possesses coercive force, or magnetic rigidity, and a steel ring would show more of it. The molecules of the iron or steel take a set. If we were to cut the soft iron ring, or separate it in any way, this introduction of resistance of air for ether in the magnetic circuit would cause the lines to collapse and set up a current in the conductor. The energy of the ring would have been restored to the latter. The curious thing is that physically the polarized ring does not present any different appearance or ordinary properties different from those of a plain ring, and will not deflect a compass needle. Its condition is discoverable, however, by the test of self-induction to currents of different direction. As a practical consideration, we may mention in this connection that a self-inductive coil for currents of one direction must be constructed differently from one to be used with alternating currents. The former must have in its magnetic circuit a section of air or the like, or be an imperfectly closed circuit, as it were. The latter should have as perfectly closed a magnetic circuit as can be made. We see here also the futility of constructing a Ruhmkorff core coil on the closed iron magnetic circuit plan, because the currents in the primary are interrupted, not reversed.

The considerations just put forward in relation to the closed iron ring, and its passive character under the condition of becoming polarized, are more important than at first appears. It has been found that the secondary current wave of a closed iron circuit induction coil or transformer, whose primary circuit receives alternating current, is lagged from its theoretical position of 90 degrees behind the primary wave an additional 90 degrees, so that the phases of the two currents are directly opposed; or the secondary current working lamps only in its circuit is one half a wave length behind a primary, instead of a quarter wave length, as might have been expected.

But when it is understood that the iron core polarized in one direction by the primary impulse does not begin to lose its magnetism when that impulse simply weakens, but waits until an actual reversal of current has taken place, it will be seen that the secondary current, which can only be produced when magnetic lines are leaving the core and cutting the secondary coil, or when the lines are being evolved and passing into the core from the primary coil, will have a beginning at the moment the primary reverses, will continue during the flow of that impulse, and will end at substantially the same time with the primary impulse, provided the work of the secondary current is not expended in overcoming self-induction, which would introduce a further lag. Moreover, the direction of the secondary current will be opposite to that of the primary, because the magnetic circuits which are opened up by the primary current in magnetizing the core, or which are closed or collapsed by it in demagnetizing the core, will always cut the secondary coil in the direction proper for this result. Transformers of the straight core type with very soft iron in the cores and not too high rates of alternation should approximate more nearly the theoretical relation of primary and secondary waves, because the magnetic changes in the core are capable of taking place almost simultaneously with the changes of strength of the primary current. This fact also has other important practical and theoretical bearings.

Let us assume a plain iron core, Fig. 7, magnetized as indicated, so that its poles, N, S, complete their magnetic circuits by what is called free field or lines in space around it. Let a coil of wire be wound thereon as indicated. Now assume that the magnetism is to be lost or cease, either suddenly or slowly. An electric potential will be set up in the coil, and if it has a circuit, work or energy will be produced or given out in that circuit, and in any other inductively related to it. Hence the magnetic field represents work or potential energy. But to develop potential in the wire the lines must cut the wire. This they can do by collapsing or closing on themselves. The bar seems, therefore, to lose its magnetism by gaining it all, and in doing so all the external lines of force moving inward cut the wire. The magnetic circuits shorten and short-circuit themselves in the bar, perhaps as innumerable molecular magnetic circuits interior to the iron medium. To remagnetize the bar we may pass an electric current through the coil. The small closed circuits are again distended, the free field appears, and the lines moving outward cut across the wire coil opposite to the former direction and produce a counter potential in the wire, and consequent absorption of the energy represented in the free field produced. As before studied, the magnetism cannot disappear without giving out the energy it represents, even though the wire coil be on open circuit, and therefore unable to discharge that energy. The coil open-circuited is static, not dynamic. In such assumed case the lines in closing cut the core and heat it. Let us, however, laminate the core or subdivide it as far as possible, and we appear to have cut off this escape for the energy. This is not really so, however. We have simply increased the possible rate of speed of closure, or movement of the lines, and so have increased for the divided core the intensity of the actions of magnetic friction and local currents in the core, the latter still receiving the energy of the magnetic circuit. This reasoning is based on the possibility in this case of cutting off the current in the magnetizing coil and retaining the magnetic field. This is of itself probably impossible with soft iron. That the core receives the energy when the coil cannot is shown in the well known fact that in some dynamos with armatures of bobbins on iron cores, the running of the armature coils on open circuit gives rise to dangerous heating of the cores, and that under normal work the heating is less. In the former case the core accumulates the energy represented in the magnetic changes. In the latter the external circuit of the machine and its wire coils take the larger part of the energy which is expended in doing the work in the circuit. In this case, also, the current in the coils causes a retardation of the speed of change and extent of change of magnetism in the iron cores, which keeps down the intensity of the magnetic reaction. In fact, this retardation or lag and reduction of range of magnetic change may in some machines be made so great by closing the circuit of the armature coils themselves or short-circuiting them that the total heat developed in the cores is much less than under normal load.

I wish now, in closing, to refer briefly to phenomena of moving lines of force, and to the effects of speed of movement. In order to generate a given potential in a length of conductor we have choice of certain conditions. We can vary the strength of field and we can vary the velocity. We can use a strong field and slow movement of conductor, or we can use a weak field and rapid movement of the conductor. But we find also that where the conductor has large section it is liable to heat from eddy currents caused by one part of its section being in a stronger field than another at the same time. One part cuts the lines where they are dense and the other where they are not dense, with the result of difference of potential and local currents which waste energy in heat. We cannot make the conductor move in a field of uniform density, because it must pass into and out of the field. The conditions just stated are present in dynamos for heavy current work, where the speed of cutting of lines is low and the armature conductor large in section.

But we find that in a transformer secondary we can use very large section of conductor, even (as in welding machines) 12 to 15 square inches solid copper, without meeting appreciable difficulty from eddy currents in it. The magnetic lines certainly cut the heavy conductor and generate the heavy current and potential needed. What difference, if any, exists? In the transformer the currents are generated by magnetic field of very low density, in which the lines are moving across the conductor with extreme rapidity. The velocity of emanation of lines around the primary coil is probably near that of light, and each line passes across the section secondary conductor in a practically inappreciable time. There is no cause then for differences of potential at different parts of the section heavy secondary. Then to avoid eddy currents in large conductors and generate useful currents in them, we may cause the conductor to be either moved into and out of a low density field with very great speed, or better, we must cause the lines of a very low or diffused field to traverse or cut across the conductor with very high velocity.

It is a known fact that, in dynamos with large section armature conductors, there are less eddy currents produced in the conductors when they are provided with iron cores or wound upon iron cores than when the conductors are made into flat bobbins moved in front of field poles. Projections existing on the armature between which the conductors are placed have a like effect, and enable us to employ heavy bars or bundles of wire without much difficulty from local currents. The reason is simple. In the armatures with coils without iron in them, or without projections extending between the turns, the conductor moves into and out of a very dense field at comparatively low velocity, so that any differences of potential developed in the parts of the section of conductor have full effect and abundant time to act in setting up harmful local currents. In the cases in which iron projects through the coil or conductor, the real action is that the lines of the magnetic circuits move at high speeds across the conductor, and the conductor is at all times in a field of very low density. Figs. 8 and 9 will make this plain. In Fig. 8 we have shown a smooth armature surface, having a heavy conductor laid thereon, and which is at a just entering a dense field at the edge of the pole, N, and at b leaving such field. It will be seen that when in such position the conductor, if wide, is subjected to varying field strength, and moves at a low speed for the generation of the working potential as it passes through the field, thus giving rise to eddy currents in the conductor.

In Fig. 9 the conductors are set down between projections, in which case both armature and field poles are laminated or subdivided. As each projection leaves the edge of field pole, N, the lines which it had concentrated on and through it snap backward at an enormous speed, and cross the gap to the next succeeding projection on the armature, cutting the whole section of the heavy armature conductor at practically the same instant. This brisk transfer of lines goes on from each projection to the succeeding one in front of the field pole, leaving a very low density of field at any time between the projections. The best results would be obtained when the armature conductor does not project beyond or quite fill the depth of groove between the projections. Of course there are other remedies for the eddy current difficulty, notably the stranding and twisting of the conductor on the armatures so as to average the position of the parts of the compound conductor.

Perhaps the most extreme case of what may be called dilution of field by projections and by closed magnetic circuits in transformers would be that of a block of iron, B, Fig. 10, moved between poles, N and S, and having a hole through it, into and through which a conductor is carried. The path through the iron is so good that we can scarcely consider that any lines cross the hole from N to S; yet as B moves forward there is a continual snapping transfer of lines from the right forward side of the hole to the left or backward side, cutting the conductor as they fly across, and developing an electromotive force in it. I have described this action more in detail because we have in it whatever distinction in the manner of cutting the lines of the field is to be found between wire on smooth armatures and on projection armatures and modifications thereof; and also between flat, open coils passing through a field and bobbins with cores of iron. The considerations advanced also bring out the relation which exists between closed iron circuit transformers and closed iron circuit (projection) dynamos, as we may call them.

I had intended at the outset of this paper to deal to some extent with the propagation of lines of magnetism undergoing retardation in reference to alternating current motor devices, transformers with limited secondary current, or constant average current, an alternating motor working with what I may term a translation lag, etc.; but it was soon found that these matters must remain over for a continuation of this paper at some future time. My endeavor has been in the present paper to deal with the lines of force theory as though it were a symbol of the reality, but I confess that it is done with many misgivings that I may have carried it too far. Yet, if we are to use the idea at all it has seemed but right to apply it wherever it may throw any light on the subject or assist in our understanding of phenomena.

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ELECTRIC LIGHTING AT THE PARIS EXHIBITION--THE OERLIKON WORKS.

Immediately on entering the Machinery Hall by the _galerie_ leading from the central dome, and occupying a prominent position at the commencement of the Swiss section, is a very important plant of dynamos, motors, and steam engines, put down by the Oerlikon Works, of Zurich. During the time the machinery is kept running in the hall, power is supplied electrically to drive the whole of the main shafting in the Swiss section and part of that in the Belgian section, amounting in all to some 200 ft., a large number of machines of various industries deriving their power from these lines of shafting, while during the evening a portion of the upper and lower galleries adjoining this section is lit by some twenty-five arc lamps run from this exhibit. Steam is supplied from the Roser boilers in the motive power court. The whole of the generating plant is illustrated in one view, and a separate view is given of the motor employed to drive the main shafting, this latter view showing the details of connection to the same. On the extreme right hand side of the first view is a direct coupled engine and dynamo of 20 horse power, a separate cut of which is given in Fig. 3. The engine is of the vertical single cylinder type, standing 5 ft. high, and fitted, as are the other two engines exhibited, with centrifugal governor gear on the fly wheel, acting directly on the throw of the cutoff valve eccentric. The two standards, supporting the cylinder and forming the guide bars, together with the entire field magnets and pole pieces of the dynamo, and the bed plate common to both, are cast in one piece.

The machine is specially designed for ship lighting, and with the view of preventing any magnetic effect upon the ship's compass, the field is arranged so that the armature, pole pieces, and coils are entirely inclosed by iron. Any tendency to leakage of magnetic lines will therefore be within the machine, the iron acting as a shield. This build of field--shown in Fig. 3A--is also advantageous as a mechanical shield to the parts of the machine most likely to suffer from rough handling in transport, and it will be seen that the field coils are easily slipped on before the armature is mounted in its bearings.

The winding is compound, and in such a direction that the two opposite horizontal poles have the same polarity; it follows from this that there will be two consequent poles in the iron, these being opposite in name to the horizontal poles and at right angles to them, viz., above and below the armature. Opposite sections of the commutator are connected together internally as in most four-pole machines, so that only two brushes are necessary, at 90 deg. apart.

The section of iron in the field is 60 square inches and rectangular in form, and the whole machine measures 4 ft. 3 in. in length, and 2 ft. in height, without including the height of the bed plate. The armature is 17 in. in length and the same in diameter, measured over the winding, and develops at the machine terminals 70 volts and 200 amperes at 480 revolutions. The moving parts of the engine are well balanced, and run remarkably well and without noise at this high rate of speed.

This dynamo serves to develop power to run a motor in an adjoining inclosure, containing some fine specimens of lathes and machine tools constructed by the Oerlikon Works. These are driven by the motor through the medium of a countershaft, and the power and speed are controlled from the switch board seen at the left of the exhibit, and in Fig. 11. The resistance, R1, serves to vary the intensity of the shunt field of the dynamo, the volts being indicated by the voltmeter V1, and a resistance separate from the switch board is inserted in the main circuit of the two machines. The ammeter, A2, is directly connected to the dynamo, and therefore indicates the current, whatever circuit this machine is running.

A larger combined engine and dynamo, seen in the center of the stand, serves to run the lighting of the galleries. The engine is a 60 horse power compound, running at 350 revolutions, and fitted with a governor on the fly wheel, like that described above.

The dynamo is a two-pole machine, the upper pole and yoke being cast in one, and the lower pole, yoke, and combined bed plate forming a separate casting. The two vertical cores, over which the field bobbins are slipped, are of wrought iron, and are turned with a shoulder at either end, the yokes being recessed to fit them exactly. The cores are then bolted to the yokes vertically from the top and horizontally below. The field of this machine is shunt-wound, and in order to maintain the potential constant a hand-regulated resistance--R2 on the switch board--is added in circuit with the shunt field. The voltmeter, V2, immediately above this resistance, serves to indicate the difference of potential at the machine terminals. Both voltmeters are fitted with keys, so that they are only put in circuit when the readings are taken.

The main terminals of this machine are fitted on substantial insulating bases, fixed one at each end of the top yoke. These connect to the external circuit by a heavy cable--the machine being capable of developing 500 amperes--and to the shunt circuit, and regulating resistance by small wires; while the two connections to the brushes are by four covered wires in parallel on each side. This mode of connection is more flexible than a short length of heavy cable, and looks well, the wires being held neatly together by vulcanized fiber bridges. The dynamo is a low tension machine, the field being regulated to give 65 volts when running the lamp circuits.

The illustration, Fig. 10, represents the automatic re-regulator--C.E.L. Brown's patent. Motion is imparted to the cores of two electro-magnets at the ends by the pulleys, W W1. The cores have a projection opposite to the spindle, ab, which latter is screw-threaded. By a relay one or other electro-magnet is put in action, and the rotating core, which is magnetized, causes rotation of the spindle by attraction, resulting in the movement of the contact along the resistance stops. The relay is acted upon directly by the potential of the dynamo, and the variable resistance is included in the shunt field of the machine, so that changes in the potential, resulting from changes in load or speed, are compensated for.

The arrangements of the lamp circuits and the lamp itself may now be described. The lamps are all run in parallel circuit, but are divided into groups of five, each group being controlled by a separate switch on the board--Figs. 11 and 11A. These switches are not in direct communication with the dynamo, but make that connection through a large central switch, S2, which therefore carries the whole current. The returns from each group are brought to the connections seen between the two resistances, where the circuits may be disconnected if desired, and the main current then passes through the ammeter, A3, to the other terminal of the machine. One of the smaller switches at the top, Fig. 11A, is directly connected with one terminal of the 20 horse power dynamo before mentioned, and the other side of the switch to the motor in the machine tool exhibit. Also one of the switches in connection with the central switch, S2, is connected to the same motor, and therefore the latter may be run by either machine, or, in fact, any combination of machines, lamps, and motor be made as required.

The form of switch made by the Oerlikon Works is illustrated in Fig. 7. Two thick semicircular bands of copper are screwed at one end to opposite sides of a square block which is turned round by the switch handle. The block has a projection at each corner, and two strong, flat, stationary springs are attached to the framework of the switch and press on opposite sides of the block. The ends of the springs engage in the projections and prevent the switch being turned round the wrong way, while the pressure of the springs on opposite sides forces the copper bands to take up a position exactly in line with the terminal contacts when the switch is closed, or at right angles to them when it is opened.

Further, each lamp has its own separate adjustable resistance, fuse, and switch. These are of special construction, combined in one, and are illustrated in Figs. 4 and 4A; the other figures, 4B and 4C, showing some of the details of the same. The wires, W W, lead from and to one lamp. The current enters at one wire, passes through the fuse, f--Figs. 4C and 4A--down the center of the cylinder to a divided contact, into which a switch arm can be shot. When this is so, a connection is made to the upright brass rod, T, which serves to grip the band, R, passing round the body of the cylinder. The current then passes through all the turns of wire above the band, and out at the other terminal. The resistance can be varied by raising or lowering the band. Fig. 4B shows the manner of tightening the band against the wires on the cylinder. The upright rod, T, is seen in section, and is fixed in one position to the frame of the apparatus. Abutting against this, and working in the block to which the two ends of the band are screwed, is a thumb screw, S, by turning which the band may be loosened for adjusting, and tightened when the right position is found. The cylinder is covered with asbestos sheet, and the wire, which is of nickel, and measures altogether from 3 to 4 ohms, is wound helically round this. The switch arm, to which the handle is attached below, does not itself make and break the circuit, but carries a spring, as shown, which, when the arm is at the end of its movement, pulls over the contact lever with a rapid action, shooting the same between the divided contact piece, and making a perfect contact. The switchboard forms one side of a closed wooden case or cupboard, with sufficient room for a man to enter and adjust the resistances or switches for each lamp. These are screwed to the inside of the case in rows, to the number of twenty-five. The greatest care has been taken in the fixing of the connections to the inside of this case, and no leading wires of different potential are allowed to cross each other.

The Oerlikon lamp, which is designed to work with constant potential, is shown partly in section in Fig. 8. There is only one solenoid, A, through which all the current passes, and whose action is to strike the arc and maintain the current constant. The soft iron core, C, is suspended from the inside of the tube, T, in which it has an up and down movement checked by an air piston in the tube. An end elevation of the brake wheels and solenoid is given in Fig. 9, where it will be seen that the spindle carrying these wheels also carries between them a pinion engaging with the rack rod, R. The top carbon attached to the rack rod falls by its own weight, and is therefore in contact with the lower carbon before the lamp is switched in circuit. When this is done the core is instantly magnetized, and attracted to the soft iron brake wheels, which it holds firmly. The air cushion in the tube prevents the core being drawn up until it has fairly gripped the sides of the wheels. The subsequent raising of the core therefore turns the wheels, raises the rack rod, and strikes the arc. The feed is operated by the weakening of the magnetic field of the coil, which causes the core to lose its grip of the wheels, and allows the top carbon to descend. The catch, L, Fig. 8, has a lateral play, and serves to engage in the teeth of the rack rod, so as to prevent its falling when being trimmed. Each carbon when in position is held against two rectangular guide bars by the pressure of a wire spring--see figure. In this way the carbon is pressed against two parallel knife edges, and is therefore always in true alignment. The action of the lamp is very simple, the working parts are few and solidly constructed, and the regulation, as exhibited by the lamps running in the galleries, is exceptionally steady.

The transmission of power plant consists of two 250 horse power dynamos--C.E.L. Brown's patent--the generator being driven by a vertical compound condensing engine of the same power, running at 180 revolutions. The dynamo generator is a four-pole 600 volt direct current machine, series wound, and may be distinguished in the engraving next to the switch board; while the motor receiver connected to it, and erected in another portion of the Swiss section, is of exactly the same size and type. The field, which is hexagonal in shape, is cast in two pieces, bolted together horizontally, the cross-sectional area of iron being 170 square inches. The armature is cylindrical, and built up of flat rings stamped out of soft sheet iron, eight notches in the same being provided to fit over the arms of the spider keyed to the shaft. The spider is in halves, which are bolted together longitudinally after the rings are in position. It is Gramme wound, and measures over the winding 7 in. radial depth, 37 in. outside diameter, and 22 in. in length. The current is collected by four brushes. The fitting and mechanical build of the dynamos leaves nothing to be desired. All the working parts of the dynamos and engines are turned up to gauge and template, so as to be interchangeable. As an instance of this, the armature of the generator was built in the works, while the field magnets were being erected in the exhibition, and, on arrival, fitted in position perfectly, and ran at once without trouble.

The energy taken off on the motor shaft is close on 200 horse power, but varies according to the machines at work; the speed of the motor does not, however, vary more than 3 per cent., and the brushes need no adjustment. About 6 ft. of shafting is coupled on in line with the motor shaft, and an extra plummer block fixed at the end. This shafting carries at its extremity an additional 2 ft. pulley, the power being delivered by belting from these pulleys to two large pulleys on the main shaft.

The machines run by this transmission consist of the looms of Rieter & Co., of Winterthur; the large flour mill and lift of A. Millot & Co.; the flour milling machinery of Frederick Wegmann & Co., of Zurich; the brick and tile making machines of the Rorschach foundries; and the looms of Messrs. Houget & Teston, of Verviers, in the Belgian section. A 15 horse power two-pole Oerlikon dynamo is also run by a belt from the main shaft, and generates power to drive a motor of similar type in the Swiss section of the upper gallery. This runs a length of countershafting supplying power to three silk-weaving machines constructed by Benninger Frères; six weaving machines from the Ruti works, near Zurich; and one knitting machine exhibited by Edward Dubied & Co., of Couvet.

The dynamo and motor are connected to the main cable by switches of the type shown in Fig. 5. These are specially designed to destroy the extra current on breaking circuit by the formation of an arc which gradually increases the resistance till the break occurs, rendering it less sudden. One wire passes through the handle and makes contact with the springs, and the other is attached to the clamp in which the carbon rod is held. The current is made to enter at the carbon rod, so that the arcs formed cause consumption of the carbon. A magnetic cut-out--Fig. 6--is also provided to each machine; this consists of an electro-magnet, through which the main current passes, provided with side pole pieces. A flat soft iron plate armature is hinged so as to come up against the pole pieces when attracted. When the current is not sufficiently strong to cause the plate to be attracted, a hole in the center of the latter engages over a small projection in the top of a weighted arm hinged in the center of the board, and keeps it upright. If now the current exceeds the limits of safety to the machine, due to a too heavy load being thrown on, the armature is attracted and releases the vertical arm, which falls over and enters with considerable force between the two spring contacts below. These contacts are connected to the field terminals, which are, therefore, short-circuited, and prevent the dynamo generating any current. A retractile spring can be adjusted to cause cut-off at any required current. These details are indicated in our illustrations mounted on their respective switch boards.

Since the erection of plant by these works at Solothurn for transmitting 50 horse power five miles distant, which attracted so much interest some time ago, several important works have been carried out. Among these we may mention a 280 horse power transmission at 1½ kilom. distance to a cotton mill at Derendingen in Switzerland, a 250 horse power transmission at ½ kilom. distance, carried out for Gaetano Rossi at Piovene in Italy, and a 300 horse transmission at 6 kilom. distance installed for Giovanni Rossi, in which the power is given off at two different stations.--_The Engineer._

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THE ADER FLOURISH OF TRUMPETS.

Although telephonic novelties are not numerous at the Universal Exposition, telephony--that quite young branch of electric science--is daily the object of curious and interesting experiments which we must make known to our readers, a large number of whom were not yet born to scientific life when the experiments were made for the first time at Paris in 1881; and it is proper to congratulate the Société Générale des Téléphones on having repeated them in 1889 to the great satisfaction of the rising generation.

We allude to the Ader system of telephonic transmissions of sounds in such a way that they can be heard by an audience.

The essential parts of this mode of transmission consist of two distinct systems--transmitters and receivers.

The transmitters are four in number, and are actuated by the same number of musicians, each humming into them his part of the quartet (Fig. 1). This transmitter, represented apart in elevation and section in Fig. 2, is identical with the one used in the curious experiment with the singing condenser. At A is a mouthpiece before which the musician hums his part as upon a reed pipe. He causes the plate, B, to vibrate in unison with the sound that he emits, and this produces periodical interruptions of varying rapidity between the disk, B, and the point, C. The button, D, serves to regulate the distance in such a way that the breakings of the circuit shall be very complete and produce sounds in the receivers as pure as allowed by this special mode of transmission, in which all the harmonics are systematically suppressed in order to re-enforce the fundamental.

This transmitter interrupter is interposed in the circuit of a battery of accumulators, with the five receivers that it actuates, in such a way that the four transmitters and five receivers form in reality four groups of distinct autonomous transmission, the accordance of which is absolutely dependent upon that of the artists who make them vibrate.

The five receivers are arranged over the front door of the telephone pavilion, near the Eiffel tower (Fig. 3). Each consists of a horseshoe magnet provided, between its branches, with two small iron cores having a space of a few millimeters between them (Fig. 4). Each of these soft iron cores carries a copper wire bobbin, N, the number of spirals of which is properly calculated for the effect to be produced. Opposite the vacant space left by the two cores, there is a small piece, t, of rectangular form, and also of soft iron, fixed to a vibrating strip of firwood, L, of about 4 inches section. The periodical breaking of the circuit produced by the transmitter causes a variation in the magnetization of the iron cores of the five receivers and makes the firwood strips vibrate energetically. These vibrations are received and poured forth as it were in front of the telephone pavilion, by large brass trumpets arranged in front of each receiver, as shown in Fig. 3.

It would be difficult for us to pass any judgment whatever upon the musical and artistic value of these transmissions of trumpet music to a distance; we prefer to confess our incompetency in the matter. But it is none the less certain that these experiments are having the same success that they had at their inception in 1881 at the Universal Exposition of Electricity, and they allow us to foresee that there is a time coming in which it will be possible to transmit speech to a distance with the same intensity that the present trumpet flourishes have. Although all the tentatives hitherto made in this direction have not given very brilliant results, we must not despair of attaining the end some day or other. Less than fifteen years ago the telephone did not exist; now it covers the world with its lines.--_La Nature._

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NOTES ON DYEWOOD EXTRACTS AND SIMILAR PREPARATIONS.

By LOUIS SIEBOLD, F.I.C., F.C.S.

During the last ten years there has been an enormous increase in the production of these preparations, and the time will come when their application in dyeing and calico printing will become so general as to completely supersede the employment of the raw materials. The manufacture of these extracts, to be thoroughly successful, requires to be so conducted as to secure the perfect exhaustion of the dyewoods without the slightest destruction or deterioration of the coloring matters contained in them; and though nothing like perfection has been reached in the attainment of these objects, it is certain that the processes of extraction and evaporation now employed by the best makers are a very great improvement on the older methods. Indeed, there is no difficulty nowadays in procuring dyewood extracts of high excellence if the consumer is willing to pay a price for them corresponding to their quality, and knows how to avail himself of the aid of chemical skill to control his purchases. Unfortunately, however, there is so much hankering after cheap articles, and so little care is taken to ascertain their real quality, that every scope is afforded to the malpractices of the adulterer. There are many dye and print works in which large quantities of these extracts are used without being subjected to trustworthy tests. Moreover, much of the testing is done by fallacious methods and often by biased hands. So fallacious, indeed, are some of these tests, that grossly adulterated extracts are often declared superior to the purer ones, the cause of this being the application of an insufficient proportion of mordant in the dyeing or printing trials, and the consequent waste of the excess of coloring matter in the case of the purer preparation.

Professional analytical chemists have hitherto given but little attention to these preparations, and the employment of experienced chemists in works is as yet far from general. The testing of dyewood extracts in such a manner as to throw full light on their purity, the quality of raw material from which they are prepared, their exact commercial value their suitability for special purposes, and the proportion and nature of any adulterants they may contain, is of course a difficult and tedious task, and must be left to the expert who is in possession of authentic specimens prepared by himself of all the different extracts made from every variety and quality of raw materials, and who combines a thorough knowledge of experimental dyeing and printing with a large experience in the chemical investigation of these preparations. But when the object of the testing is merely careful comparison of the sample in question with an original sample or previous deliveries, the case is much simplified, and comes within the scope of the general chemist or the laboratory attached to works. A few years ago I recommended carefully conducted dyeing trials on woolen cloth mordanted with bichromate of potash as the best and simplest mode adapted to such cases, and my subsequent experience enables me to confirm that observation to the fullest extent. Most of these extracts contain the coloring matter in two states, the developed and the undeveloped, and an oxidizing mordant such as bichromate of potash causes the latter as well as the former to enter completely into combination with a metallic base; whereas many of the other mordants, such as alumina or tin compounds, merely take up the developed portion of the coloring matter together with such small and variable proportions of the undeveloped as might undergo oxidation during the process of dyeing. I would therefore suggest dyeing trials with alumina, tin, iron, etc., only as subsidiary tests indicating the suitability of an extract for certain special purposes, while recommending the trial with bichromate of potash as the one giving the best information respecting the actual strength of the extract in relation to the raw material from which it was obtained, and as giving a fair idea of the money value of the sample. Cotton dyeing does not, as a general rule, afford a good means of assaying extracts, as it is generally done under conditions which do not admit of complete exhaustion of the dye bath, but it might often with advantage be resorted to as an additional trial throwing further light on the degree of oxidation or development of the coloring matter. Printing trials are apt to give fallacious results unless the proportion of mordant is carefully adjusted to the amount of coloring matter present, and several trials with different proportions would be necessary to prevent erroneous conclusions. For the trials with bichromate of potash on wool I would recommend pieces of cloth weighing about 150 grains, and the most suitable proportion of bichromate of potash is 3 per cent. of the weight of the cloth. The requisite number of pieces (equal to the number of samples to be tested) should be thoroughly scoured and then heated in the bichromate solution at or near the boiling point for not less than 1½ hours, after which they should be well washed and then dyed separately in the solutions of equal weights of the extracts at the same temperature and for the same length of time; 15 grains of extract is a suitable quantity for a first trial under these conditions. These trials can then be repeated with different relative proportions of extract in order to ascertain what weight of a sample would give the same depth of color as 15 grains of the standard example. Many precautions are required both in the mordanting and dyeing processes in order to obtain trustworthy results; and though the trials with bichromate of potash give the most reliable information of any single test, they should be supplemented by the subsidiary tests already alluded to, and also by a chemical examination, in order to obtain a knowledge, not merely of the wood strength, but also of the general nature of the extract. An adulteration with molasses or glucose can be best determined by fermentation in comparison with a pure sample. Mineral adulterants may, of course, be detected by an estimation and analysis of the ash, after making due allowances for variations due to differences in different kinds of the same dyewoods. The estimation of the individual coloring matters in these extracts by means of a chemical analysis is under all circumstances a task requiring much experience, especially as the coloring principles are associated in different qualities of each class of dyewood with different proportions of other constituents which often give much trouble to the unpracticed experimenter. Extracts made from logwood roots are now largely manufactured and often substituted or mixed with the extracts of real logwood, and have in some instances been palmed of as logwood extracts of high quality. The correct determination of such admixtures, like the fixing of anything like the exact commercial value of dyewood extracts, requires nothing less than a complete chemical investigation coupled with numerous dyeing trials in comparison with standard preparations, and should be left to an expert.

The presence in dyewood extracts of coloring matters in various stages of development has hitherto militated against their use in place of the raw materials by many dyers and printers who are still employing inherited and antiquated processes in which the whole of the coloring matter is not rendered available. It is often asserted by these that even the best of extracts fail to give anything like the results attained by the use of well-prepared woods, and that, indeed, their application proves a complete failure. Such failure, however, is simply due to the want of chemical knowledge on the part of the dyers, for there is no real difficulty in making any good and pure extract serve all the purposes for which the woods were used. It is to be hoped that in this branch of industry, as well as in many others, the employment of chemists will become more general than at present, and not be restricted, as is often the case, to young men without experience and without the trained intellect so essential to success in chemical investigations. High class chemical skill is of course available to the manufacturer, but the man of science who brings matured knowledge and valuable brain work into the business required social as well as pecuniary recognition, and the sooner and more fuller this fact is appreciated the better it will be for the maintenance and progress of our industries.

With regard to the astringent extracts, such as sumac, myrabolam, divi, valonia, quebracho, oak, etc., it is the aim of the manufacturer, whenever such extracts are intended for the purposes of dyeing and printing, to obtain the tannin in a form in which it is best calculated to fix itself upon the fiber. The case is somewhat different when the same extracts are required for tanning. For this purpose it is necessary that the extract shall have considerable permeating power, and that the tannin contained in it shall readily yield leather of the desired texture, color, and permanency. Extracts specially suited for this purpose are by no means always the most suitable for the dyer, and _vice versa_.

A brief description of the processes by which the astringent extracts may be tested with particular reference to their fitness for definite purposes concluded the paper.