AUGUST 23, 1889.]

without creating any difference in the luminosity of far and near lamps, while an extension of the area of supply within certain limits necessitates only a length of additional wire sufficient to take in the lamps. But this is true only so long as a certain voltage is not exceeded, for obviously we cannot extend the area and increase the E.M.F. indefinitely. The highest E.M.F. employed by the Heisler Company up to the present time is 3,000 volts, and we imagine that with this voltage the limit is reached, so far as safety is concerned; in fact, many would say it is overreached. The lamps are of 30 candle-power, nominal, and require each 14 volts, so on a single circuit there can be placed, allowing for the resistance of the line, something like 212 lamps in series. Now, when it is wished to extend beyond this number, another circuit must be erected, and if the extension is in the direction of the existing lamps, it means that the new circuit will lie alongside the one already up, this being in all respects equivalent to increasing the area of a main for extension when feeding transformers on the parallel system. It is easily seen that neglecting the loss in transformers, for a given weight of copper in mains and branches the loss in distribution is the same for a

207

being built for differences of potentials up to 3,000 volts, and to run at speeds from 600 to 800 revolutions per minute. The machine exhibited gives, at its normal speed of 640 revolutions, 1,750 volts on each 5 ampères circuit, supporting therefore 125 lamps in series or generating current for 250 lamps in all. These lamps are said to give a light of 30 candles each, but of this we could not judge by day. Thirty candles certainly seem a great deal for an expenditure of 70 watts, even when we remember that low voltage lamps can, without detriment, be run at higher efficiency than those of high voltage. The armature of the alternator, A, B, fig. 2, is built of wrought iron plates, in eight sectors, these being held in position by insulated phosphor bronze rods, secured to the two end frames. There are 32 coils in all, each sector being wound with four, as shown, and alternate coils being included in the same circuit. It will be seen that on withdrawing the phosphor bronze rods the sectors, with their coils, can easily be removed. The radial magnets are 16 in number, and fastened with their poles alternately, N and s, on a 16-sided cast iron cylinder. The coils in each circuit are equal in number to the magnet poles, and as the surface of the armature is almost wholly covered by the winding, the coils

number of lamps supplied with current on the Heisler system, as for the same number supplied on the parallel system, provided the difference of potentials at the dynamo terminals is in each case similar. But while in the parallel system the difference in the brightness of far and near lamps depends on the size of the mains or on the E.M.F. wasted in them, in the series system all the lamps are of uniform brightness, and remain unaffected by any loss over the circuit. This constitutes the strongest argument in favour of a series system, but we must leave our readers to make any further comparisons they have a mind to between it and the better known system of distribution by transformers. It must be remembered that the loss in the transformers, amounting to three watts per 70-watt lamp when fully loaded and perhaps 10 watts when lightly loaded, must be debited to the latter system.

The Heisler dynamo shown in fig. 1 is of the alternating current type, having a stationary ring armature and revolving radial magnets. On the shaft carrying the latter is fixed the armature of the exciter, which is Gramme-wound, and rotates in a four-pole field, both alternator and exciter being surrounded by a sheet iron casing as shown. The armatures of all sizes are wound in two circuits, each carrying 5 ampères, the machines

of one circuit occupy about half the surface, and have between them spaces in which the coils of the second circuit are wound.

The reason for winding the armature in two circuits will now be apparent. It is evident that when the E.M.F. of one set of alternate coils is maximum, that of the other is 0, or in other words, the induction phase of one circuit is a quarter cycle behind the other. Suppose the curves, A and B, fig. 3, to represent the E.M.F.s induced in the two circuits, time being represented by abscissæ. With the two sets of coils supplying different circuits of lamps, the total E.M.F. available is at any instant the sum of these two E.M.Fs., independent of their direction, and may be represented. by the top wavy line, C, C1, C. But if the two circuits were coupled in series, the E.M.F. would, at any time, be the sum of the two curves, with the direction of one considered plus and minus accordingly as it is aiding or opposing the other. Plotting out a curve to represent this result we get the line, D, C, D, C, the area enclosed by the induction curve being now much less than when the two circuits were independent of each other. We have lost the area shown by the darker hatched portion, and this shows clearly that part of the winding induces an E.M.F. in an

run separately. The ratio of the two outputs must depend on the disposition of the iron parts and several other things, the value here given not necessarily holding for other machines. It is, however, significant that in this particular alternator the E.M.F. is only increased in the ratio of 8 to 7 by doubling the width of the winding when a single circuit is employed. But by employing for his system of lighting two separate circuits and utilising the whole surface of the armature, Mr. Heisler gets nearly double the ouput from this machine for given carcase dimensions.

The

The exciter is series wound, and the current is collected by two sets of brushes 90° apart. The magnets consist of a ring surrounding the armature, on which are fixed four pole pieces, the portions between these being covered by the magnetising coils. E.M.F. of the exciting current is from 75 to 80 volts, all the inducing magnets being joined in series. From the terminals of the exciter, exterior wires pass to brushes resting on insulated rings concentric with the axle, the ends terminating the circuit of the inductors being attached to these latter.

The most interesting part of the exhibit is an automatic regulator, upon the reliability of which the working of the whole system practically depends. For supplying lamps in series the current must be kept at a constant value, and our readers will remember that in describing previous machines we explained the action of regulators which corrected in a very effective manner the tendency of the current to increase or diminish. In one such apparatus a trifling variation in the current brought mechanism into action which moved the brushes backwards or forwards on the commutator; in another it brought into action mechanism which, by moving the arm of a rheostat, shunted more

[AUGUST 23, 1889.

current must be kept constant, and it is by no means certain that there will be at the same time a similar number of lamps on each circuit.

The circuits are kept in practice as nearly even as possible, and with the two running in the same direction, and lighting alternate lamps the number alight on each may not at any time be very different; still it is possible that they may under some circumstances differ considerably, and, accordingly, provision must be made for such condition arising. It is the function of the automatic regulator to keep the current constant in two circuits which may require for their respective numbers of lamps a different voltage, the adjustment required being therefore of a two-fold character. So long as the lamps on the two circuits are varied simultaneously the E.M.F. is adjusted by moving the brushes of the exciter on the commutator which alters the exciting current. But when by varying the lamps on one circuit only, the numbers are made dissimilar, a second adjustment is effected whereby a resistance is thrown into the circuit having the less number of lamps, this resistance absorbing an E.M.F. equal to the difference in the voltage requirements of the two circuits. Both the movement of the exciter brushes and the variation of the compensating resistances in the circuits are effected by the automatic regulator.

The regulator has a somewhat complicated look, but is really a most ingenious piece of mechanism. Its various parts cannot, however, be well shown on a diagram, and we must therefore content ourselves with explaining its action in such terms as will enable our readers to form a general idea of its working. It is enclosed in a wood case placed near the dynamo, there being one for each machine. The apparatus consists first of two circles of rheostat blocks with which two arms keyed to separate horizontal spindles make contact, and by their movements vary according to requirements the resistances in the two circuits. On the other ends of these rheostat spindles are keyed toothed wheels. Close to the peripheries of these and diametrically opposite are two pawls to which a reciprocating motion is given by cams fixed on an axle driven from the dynamo shaft. The current in each circuit circulates round a laminated iron core which is thereby magnetised, its action on an armature causing one pawl or the other to engage the toothed wheel and so increase or diminish resistance if the current rises or falls. When the current is normal the pawls reciprocate without either engaging the wheel. So far the regulator for each circuit differs only in detail from another described some weeks since. But it has to perform the additional function of moving the brushes on the exciter, and ensuring moreover that in the circuit with the greater number of lamps there shall be no resistance, there being only enough in the other to absorb the difference in the volts required for the lamps on the two circuits. This means that one of the two rheostat arms should always be in the position in which it short-circuits the resistance coils. Should the arm which happens to be in this position be caused to leave it by a sudden variation in the load, mechanism is brought into action at once which sets a vertical spindle in motion to move the brushes on the exciter commutator. This raises or lowers the E.M.F., and accordingly the pawls act to vary the resistance until the rheostat arm belonging to the circuit of most lamps again short-circuits the resistauce coils. The vertical spindle referred to is geared by bevel wheels to a horizontal spindle having on its end a worm. This latter gears into teeth cut on a wheel attached to the brush carrier, which is not, however, shown in our engraving.

Outside the generating station every precaution is taken to ensure that the continuity of the circuits shall under all circumstances be maintained. If a lamp is removed or broken, an automatic device short-circuits the main, while for every consumer there is again a circuit closer, which in event of accident to the indoor wiring short-circuits the main where it enters and leaves the premises. This closer consists chiefly of a small magnet having wound on it a coil of about 200 ohms resistance. This is provided with an armature

AUGUST 23, 1889.J

which in its normal position holds back a copper bar, tending by the pull of a spring to short-circuit the mains. The coil being connected as a shunt to the house, the difference of potentials at its terminals is under normal conditions insufficient to attract the armature; but, should it rise above a certain value, the attracted armature releases the copper bar, which then flies up and effects a short-circuit.

It appears from the reports before us that the Heisler system has been installed in several towns in the States with considerable success. The company claims to obtain in working 490 watts per horse-power given to the dynamo, and in the practical erection of their circuits employ mains of such size as to lose in them 70 watts (one lamp) per mile. The details of the system have evidently been thought out very completely, and with great care.

The Edison Company, of America, has a very extensive exhibit, comprising all sorts of apparatus and appliances with which the name of the distinguished Edison has been from time to time associated. The Edison dynamo, as made by the American Company, must be well known to our readers, and an illustration is therefore unnecessary. Several machines of different sizes are shown, the largest with an output of 175,000 watts, and the smallest giving 2,500 watts. The current from the former, at a speed of 450 revolutions per minute, is 1,250 ampères, at a difference of potentials of 140 volts. This machine is rated for 2,500 lamps of 16 C.P., or 4,000 lamps of 10 C.P. The number of sections in the commutator is 41, the current being collected by six brushes on each pole, 14 inch wide by inch thick. The driving pulley is 3 feet 8 inches diameter by 21 inches wide. The machine weighs 12

tons.

We give in the following interesting table the principal dimensions of the different sizes of dynamos now being built by the Edison Company for the lighting of towns on the parallel series system. The difference of potentials is in all cases 1,200 volts, the current being divided into circuits of 3 ampères each.

MUNICIPAL SYSTEM OF EDISON.

Dimensions of Machines.

209

fundamental formulæ are established where friction is disregarded, only to be taken into account later on as a particular force. We will, therefore, endeavour to find the most general law of induction, supposing the resistance to be nil, and this method of procedure is, besides, justified à priori by the simplicity of the results, the facility of some of their applications and their agreement with recent experiments.

2. Let us suppose a circuit in which the sum of the electromotive forces is e, the resistance r, the intensity of current i, and the coefficient of self-induction L. We know that we get

If the electromotive force, e, is due solely to induction, we get d N e= d t'

N being the flow of force (or the number of lines of force) contained in the circuit; this expression of e is, besides, quite general; it is applicable to the case in which there would be at the same time variation in the external magnetic field, displacement and alteration of the circuit.

di We may express in the same way the term L at which dt' represents the electromotive force of the extra current, as a function of the flow of force, N', due to the existence of the current, i, and passing through the circuit. Taking into account the signs, we get

whence, by integration,

NN const.

Maximum number of 3 ampère

1. We know that the electromotive forces of induction are, like the electro-dynamic actions, independent of the nature of the material in which the circuit is made; and, consequently, independent of the resistance of the circuit. It follows that, if we wish to treat of the laws proper to these phenomena, we may abstract the resistance. Of course, when once the general formulæ are established they may be applied to any special case, taking into account any resistances that may occur. will proceed exactly as in applied mechanics, in which

Comptes Rendus.

We

(3)

(4)

Such is therefore the result which we obtain for r = 0, whatever may be the phenomenon of induction to be considered. In ordinary language: In a circuit without resistance, the intensity of the current induced is always such that the flow of force passing through the circuit remains constant. In other words, if the induced current did not exist, the variation of the magnetic field, the displacement, or alteration of the circuit would produce a variation, ▲ N, of the flow of force, N, which was passing through the circuit; it is this very variation that produces the induced current; the circuit being closed and without resistance, the induced current is then at each moment such that it produces an increase, ▲ N', of the flow of force, equal to ▲ N and of opposite sign. The inducing phenomenon and the induced current produce effects to a certain extent complementary. If we use the idea of lines of magnetic forces, we may express the same proposition by saying that a circuit without resistance is impermeable to the lines of force. Really, since owing to the induced current this number is invariable, it is because it is impossible to introduce into the circuit or take away from it, a single line of force.

3. As a corollary of the above theorem, we may mention a proposition which completes Lenz's law, in the case of circuits without resistance. When we displace or alter a circuit, the induced current gives rise to forces which tend, according to Lenz's law, to oppose themselves to the motion. The value of N being only a function of the parameters which define the form and position of the circuit, it is the same with N', since

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N+N' 0; consequently it is the same with the intensity, i, of the induced current; and lastly, it is the same with the electro-magnetic forces due to i. Thus these forces are functions only of the displacements as they would be of elastic forces.

In the case in which the induced circuit, in its initial position, is not traversed by any current, the electromagnetic forces due to induction tend to bring it back to this position, and only become nil when it has returned to it; this position, therefore, is that of stable equilibrium. In the same way, a magnetised needle, deviating in the presence of a circuit, is brought back by the electro-magnetic forces due to induction to the position which corresponded to no current, as to a position of stable equilibrium.

To sum up, then, a circuit without resistance behaves, from the point of view of the attractions and repulsions produced, exactly like a diamagnetic sheet magnetised by influence; and we thus arrive, in a somewhat generalised form, at the theory of diamagnetism proposed by Weber."

4. In order to show more clearly the signification of the formula N + N' constant, we may solve the two following applications.

=

First Example.-A solenoid with resistance nil bearing n turns of wire per unit of length, and traversed by no current, has at first its axis directed perpendicularly to a magnetic field of intensity, H; we bring this axis parallel to the field; what is the intensity, i, of the induced current ?

Solution. The flow of force traversing the solenoid at the commencement being nil, remains nil constantly. The value of i is then given by the equation

Second Example.-A solenoid bearing n turns of wire per unit of length is traversed by a current of intensity, i. Find the normal resultant, f, at the surface of all the electro-dynamic actions exercised by the solenoid on the elements of current covering the unit of surface. In order to solve this problem, let us imagine that the radius, R, of the solenoid undergoes a real or virtual increase, d R, and let us suppose at first that the internal magnetic flow remains constant. We then get

[AUGUST 23, 1889.

On eliminating H and U and their derivatives in the above equations, and those deduced by differentiation, we find without difficulty that

f = 2 x n2 i2.

5. Can we demonstrate experimentally that the conductors with a resistance nil act really as if they were impermeable to the lines of force? At first it may seem impossible, since it is not in our power to dimish indefinitely the specific resistance of the conductors under consideration.

However, some recent experiments of M. Hertz, instituted in this order of ideas, furnish this experimental demonstration. This physicist has shown that a metallic envelope acts as a perfect screen against extremely rapid inductive actions. Now, referring again to equation 1

we see that e, the electromotive force of induction, increases with the speed of the inductive variation; it di

If this speed increases

is the same with the term a t⋅ in the ratio of 1 to 300,000,000 (such are the numbers of variations per second utilised by M. Hertz), the two first terms are multiplied by this factor, while the term in r is independent of it, this last term then may be disregarded. It proceeds therefore as if the magnetic variation being unity, the resistance, r, were divided by a factor such as 300,000,000. And, in fact, a thickness of th a millimetre of metal seems impermeable. If r could become strictly nil, the speed of variation as well as the thickness of metal would become indifferent.

ELECTRICITY AND GAS IN LIVERPOOL.

PRESIDING on Tuesday last at the annual meeting of the Liverpool United Gas Light Company, Mr. EDWARD LAWRENCE said that in view of the somewhat serious contingencies to be faced during the year, it would not be a wise policy on the part of the board to attempt any One reduction in the price to be charged for gas. special reason why they had to be careful and to husband their resources was that during the next year they would have to face the competition of the electric light. Whilst he did not think that they had anything to fear from free and open competition with electricity, they could not shut their eyes to the fact that to a certain extent it would interfere with the consumption of gas. But he did not consider it would be to such a degree to hamper the company or to injure them. At the same time it was one of those elements they had to consider when they were dealing with the question of reducing prices. And inasmuch as during the next year they might expect some little decrease in the consumption of gas from customers who would use the electric light, he thought the public would have to be satisfied with the price remaining at its present moderate amount. The directors did not forget the advantages of cheap prices in all such things, nor the important part which cheapness played in competition, and their object was to give to the public as cheap an article as they possibly could of the quality which was required of them by Act of Parliament. However, for the present they would, he was afraid, have to maintain the price at which it now stood, because it would be the height of folly for them to reduce it to day and perhaps six months hence have to increase it. He had several times been asked as to the prospects of the company and how far it was likely it would be interfered with by electricity. They all admitted that electricity was now being rapidly pushed forward; but from all he could gather in London he did not think that electricity would interfere to any extent with the gas companies, at least to their detriment. The consumption of illuminants went on increasing year by year, and

AUGUST 23, 1889.]

although electricity might take its place, there were some branches in which it was not possible for it to compete with gas; and so long as gas remained the cheap article it was, and so long as electricity remained the dear article it was, there was no fear of the competition of electricity interfering to any detrimental extent with the manufacture of gas. Of course they could not tell what science might do in the future, but taking things as they at present stood, and looking at the initial cost of maintaining it, he did not think there was any chance of any harm being done to gas in the competition. In conclusion, he informed the shareholders that the directors were taking every possible precaution they could to see that their interests were fully protected; and as to the public, the board were doing everything they could to discharge their duty to them in supplying the gas they were bound to supply at the lowest price at which it could be obtained.

In the course of the discussion which ensued, Mr. G. H. BALL expressed disappointment at the inability of the board to reduce the price of gas, although he agreed that it would be an unwise step to do so at present. With reference to electricity, he said he had had something to do with experiments that had been made with regard to the comparative cost of gas and electricity, and the result had been decidedly in favour of gas. In fact so much so, that in one institution electricity had been abandoned. And, further, owing to the improved methods of illumination by gas, it could be used far more economically than formerly. Oil had been in another instance found to be more economical than gas; but this was where the price of gas was 5s. 6d. per 1,000 feet, whereas it was admitted that in Liverpool, where the price was 2s. 8d. to 3s., it was far more economical.

Mr. J. STOLTERFOHT spoke of the use of gas for cooking purposes, and also said that in the metropolis there was very little fear as to the introduction of the electric light having any influence on the prosperity of the gas companies.

The CHAIRMAN, in answer to a shareholder, who wanted to know the position and prospects of water gas, replied that it was not at all likely to be in the smallest degree a rival. It might be applicable for certain purposes, but for ordinary purposes water gas was of no use.

OVERHEAD WIRES.

A SET of regulations has been issued by the Board of Trade affecting certain cases in which overhead wires have been used for the supply of electricity. In the first place, no aerial conductor is to be fixed in any part of any street at a less height from the ground than 20 feet, or where it crosses a street 30 feet, or within 6 feet of any building except where it is brought into a building for the purpose of supply. The maximum intervals for the supports are fixed at 200 feet where the direction is straight, and 150 feet where it is curved, and care is to be taken that all supports are of durable material and properly stayed against forces due to wind pressure, change of direction of wires, or unequal lengths of span, the maximum possible wind pressure being taken at 50 lbs. per square foot. No addition need be made for a possible accumulation of snow. Minute regulations are made for the efficient connection of supports to earth and for the provision of lightning conductors for supports of non-conducting material. Every aerial conductor is also to be protected by efficient lightning protectors of a pattern approved by the Board of Trade. The angle of crossing thoroughfares is not to be less than 60 degrees, with spans as short as possible, and precautions are to be taken against the possibility of crossing wires coming into contact with one another. Every high pressure aerial conductor must be continuously insulated with a durable and efficient material to be approved by the Board of Trade, to a thickness of not less than

211

one-tenth of an inch, and in cases where the extreme difference of potential in the circuit exceeds 2,000 volts, the thickness of insulation must not be less in inches or parts of an inch than the number obtained by dividing the number expressing the volts by 20,000. This insulation must be further efficiently protected on the outside against injury or removal by abrasion. If this protection be wholly or partly metallic it must be efficiently connected to earth, so, however, as not to cause undue disturbance to other electric lines or works by electrostatic induction or otherwise. There are further regulations dealing with the specification of insulation, the minimum insulation resistance allowable, the suspension of conductors, the protection of telegraph and telephone wires from interference, and other detailed matters, and it is finally ordered that a notice describing every aerial conductor erected or used for the supply of energy shall forthwith upon receipt of these regulations be served upon the Postmaster-General, together with a plan showing the mode and position in which such conductor is erected, and that the Postmaster-General may require such alterations therein as he may think necessary for the protection of the works of the Post Office. Any failure to comply with his requirements is to be considered a non-compliance with the regulations.

NOTES.

Electric Lighting at Southampton.-At the last meeting of the Southampton Town Council, a letter was read from the Local Government Board with reference to the application made by the Council for sanction to borrow £1,440 for the purposes of electric lighting. The communication stated that the law officers of the Crown had been consulted as to whether local authorities were empowered to manufacture electricity for the lighting of streets, markets, and public places in their district, without obtaining a license or provisional order under the Electric Lighting Acts. Their opinion was that a provisional order must be obtained. Mr. Cleveland enquired what the cost of obtaining a provisional order would be? The Town Clerk replied that certain fees would have to be paid, but he was not certain as to the exact amount. The matter was referred to the Special and General Works Committee.

Proposed Electric Lighting in the Isle of Wight.At a meeting of the Ryde Town Council held last week, it was resolved to invite the co-operation of the other Island authorities in opposing the application of electric lighting companies to the Board of Trade for provisional orders. It was, moreover, decided that the authorities should be invited to attend a meeting to deliberate as to the best mode of opposing the applications.

The Electric Light for Harbour Defence.-During the progress of the Naval Manoeuvres the Scourge, tender to the Defiance, is anchored near the breakwater at Plymouth every night, and sweeps the sea with her search light, with the view of preventing hostile craft from approaching unseen. Search lights are also employed with the same object at Bovisand and Picklecombe Forts.

Attributed to the Electric Light.-Her Majesty's ship Warspite reached Plymouth at 12 o'clock on Monday night. As she was entering the Sound she came into collision with a Swedish barque. The Warspite was not much damaged, but found it necessary to bring the other vessel into harbour. The accident is attributed to the flashing of the electric light. much has been said for and against the use of the electric light at sea that it is really high time to ascertain for a certainty whether it is a source of real danger to the seafaring man, or whether the light is made the scapegoat of careless and blundering navigators.

So