Rail Pattern.

Solid Frame.

The speed of the armatures was determined by one of Harding's counters, in all cases a full minute being taken.

The constants of all electrical instruments were calculated for the mean temperature of the dynamo room-27° centigrade. The temperature correction for the dynamometer pulley was not determined, as only the first or last two or three readings were to be used in the results, and the accuracy of these was ensured by taking the zero of the pulley both before and after the machine was run. The intermediate readings were taken only to show if any serious alterations took place in the general working of the machines.

These tests, the results of which are tabulated (see Table A), were made primarily to ascertain the commercial efficiency of the various arc machines used. By "commercial efficiency," I mean the ratio of the electrical energy available at the terminals to the actual energy absorbed at the spindle of the machine.

[NOVEMBER 22, 189

armatures. The resistance of the voltmeter used was grati that the potential difference as shown by it was practialys electromotive force of the machine.

As the number of windings and speed of rotation of the tures were the same, the electromotive forces would be dire proportional to the total induction through the armatures.

The induction through the armatures depends on the mag ing force, H, of the current in the field coils, and the goodnes the magnetic circuit.

In the machines tested the number of windings on the S coils were equal. Hence the electromotive forces of the dif machines, when taken with the same current in the field, w. represent the relative values of their magnetic circuits.

The curves may be taken either as saturation curves of a total magnetic circuit, or as curves of total induction through armature, provided no sensible current is taken from it.

It will be seen that the current actually supplied by the majority of the machines was a little below the normal, the machines being professedly designed for a current of 10 ampères.

The times of run as shown in the table were not sufficient for the machines to attain their state of steady temperature, though in the majority of cases the temperature reached would be a fair average for ordinary working.

The armatures of the machines were interchangeable, so that any given armature cannot be considered a part of any specified machine; it was important, therefore, to ascertain not only the relative value of the different forms of frame, but also of the different armatures in them.

It will be seen from the table that the different forms of machine having thin-plate armatures are almost equally efficient, the solid frame pattern having a slight advantage. The difference, however, between the two forms of machine with thick-plate armatures is still less, and the advantage in favour of the rail pattern. But as only one of the solid-frame machines contained a thickplate armature the comparison is of little value. For practical purposes it may be said that the commercial efficiency of the two forms of machine, provided the armatures are similar, is the same. Greater alterations in the efficiency of either class may be caused hy slight alterations in the conditions of working, than the actual difference between the two classes as shown in the table.

The difference in the two types of armatures is very marked. Taking the mean from the two classes of machines, the efficiency of the thin-plate armatures will be found to be about 8.27 per cent. greater than that of the thick-plate armatures. But, unfortunately, the thin-plate armatures were not calculated to withstand the mechanical strains to which they are subjected in ordinary work, so the higher efficiency obtained from them has only a theoretical existence. There is, however, no mechanical reason why the armatures should not be constructed with thin plates, and at the same time be free from the mechanical faults shown to exist in those under review. Indeed, such armatures have been constructed in the Victorian railways telegraph workshops which are quite free from the faults named. One of these has been running for several years without ever giving trouble, and doing excellent work.

The curves in the diagram (fig. 1) were taken to ascertain the relative value of the magnetic circuits in the two classes of frames. The method adopted was as follows:

The commutator brush-holders were electrically disconnected from the field magnet circuit. The ordinary brushes were taken out and replaced by others so bent that contact could be made with the commutator at the neutral point. The armature was run at the normal speed, and the field magnets were separately excited by a variable current taken from an incandescent circuit. Simultaneous readings were taken of the current through the field coils, the potential difference at the terminals of the armature, and the speed of rotation. From these data curves were plotted as shown in the diagram.

All the machines tested in this manner had similar thin plate

Physical Society, November 15th, 1889.

Prof. REINOLD, F.R.S., President, in the chair. Prof. J. Milne and Lieut. G. F. Eyre were elected members. Mr. ENRIGHT resumed the reading of his paper “On the electr fication due to the contact of gases with liquids." Repeating be experiments with zinc and hydrochloric acid, the author by pas ing the gas into an insulated metallic vessel connected with the electrometer, proved that it was always charged with electricity of the opposite kind to that of the solution. The electrol phenomena of many other reactions have been investigated with the result that the gas whether H1, CO,, SO,, SH, or CI, is alv electrified positively when escaping from acids, and negatively

en leaving a solution of the salt. In some cases distinct reversal not obtainable, but all these seem explicable by considering the lubility and power of diffusion of the resulting salts. Various ner results given in the paper tend to confirm this hypothesis. eking for an explanation of the observed phenomena, the author uld arrive at no satisfactory one excepting "contact" between ses and liquids, and if this be the true explanation, he hoped to ove it directly by passing hydrogen through acid. In this, wever, he was unsuccessful owing, he believes, to the imposbility of bringing the gas into actual contact with the liquid. ue contact only seems possible when the gas is in the nascent ate. Some difficulty was experienced in obtaining non-electrified s, for the charge is retained several hours after its production, en if the gas be kept in metallic vessels connected to earth. ach vessels when recently filled form conductors in which the ectricity pervades an enclosed space, and whose charge is availle on allowing the gas to escape. Soap bubbles blown with wly generated hydrogen were also found to act as condensers, e liquid of which, when broken, exhibited a negative charge. his fact, the author suggested, may explain the so-called " firealls" sometimes seen during thunderstorms, for if by any normal distribution of heat, a quantity of electrified air becomes closed by a film of moisture, its movements and behaviour would osely resemble those of fire-balls. A similar explanation was roposed for the phenomenon mentioned in a recent number of ature, where part of a thundercloud was seen to separate from e mass, descend to earth and rise again. The latter part of the aper describes methods of measuring the contact potential fferences between gases and liquids, the most satisfactory of hich is a "water dropper," and by its means the P.D. between ydrogen and hydrochloric acid was found to be about 42 volts. Prof. RUCKER asked if the experiment with zinc and hydroaloric acid could be started in the second stage by having the cid partly saturated with salt.

Dr. C. V. BURTON thought it probable that contact could be made etween a gas and a liquid by shaking them up together in a ottle.

In reply, Mr. ENRIGHT said the experiment could be started at ny stage, and reversal effected as often as desired by adding ither acid or a solution of salt to the generating vessel.

The

Mr. HERBERT TOMLINSON, F.R.S., read a paper "On the Effect f Repeated Heating and Cooling on the Electrical Resistance and Temperature-coefficient of annealed Iron." In a paper recently resented to the Royal Society, the author has brought forward n instance of an iron wire which, when subjected to magnetic ycles of minute range alternately at 17° and 100° C., had its molecular friction and magnetic permeability reduced respectively o about one-quarter and one-half their original values. resent experiments were undertaken to see whether by such eatings and coolings, the temperature coefficient of iron could be rought down to something approaching the number given by Matthiessen for "most pure metals." The wire experimented on was first annealed by heating to 1,000° C. for several hours and allowing to cool slowly in a furnace placed at right angles to the nagnetic meridian; the process was repeated three times. Afterwards the wire was covered with paper and wound doubly into a coil. This coil was enclosed in a water-jacketed air chamber and connected with a sensitive Wheatstone bridge. Thermo-electric and Peltier effects were eliminated by always keeping the galvanometer circuit closed. By repeated heating to 100° C. and cooling to 17° C. for long intervals, the specific resistance at 17° C. was reduced from 11,162 to 10,688 C.G.S. units, after which the operations produced no further change. At the same time the emperature coefficient increased in the proportion of 1: 1·024 From careful determinations of the resistance at different temperatures the formula

R R. (1005131 t + 00000815 t2)

was deduced, whilst that obtained from Mathiessen's results for pure iron annealed in hydrogen is

R1

=

R. (1005425 t + 0000083 t2). Taking his own determination of specific resistance of impure iron as correct, coupled with Matthiessen's law connecting the resistances and temperature coefficients of inetals and their alloys, the author finds that the specific resistance of pure iron deduced from Matthiessen's results is from 4 to 5 per cent. too high.

In conclusion, Mr. Tomlinson expresses a hope that the B.A. Electrical Standards Committee may be induced to determine the absolute resistance and temperature coefficient of the pure metals which are in ordinary use.

Prof. AYRTON thought Matthiessen's results were expressed in B.A. units, and hence might appear 1 or 2 per cent. too great. Mr. Tomlinson, however, believed the number he took were expressed in legal ohms.

Dr. WALMSLEY asked for what value of the magnetising force the permeability of the iron mentioned in the beginning of the paper was determined; to which Mr. Tomlinson replied that they were much smaller than the earth's horizontal component. Dr. Thompson's paper on Geometrical Optics was postponed.

City Guilds Old Students Association.

'Some Peculiarities of Alternate Currents." By W. E. SUMPNER, D.Sc. Presidential Address, read at the Central Institution, November 19th, 1889.

Alternating currents are not by any means new, although it is only lately that they have become of great importance in engi

neering work. The dynamos first made yielded alternating currents, because as they needed no commutator they were simpler to construct. They were not adopted, partly because continuous currents were easier to understand and to use, and partly because direct current dynamos could be made self-exciting. Alternators came to be looked upon as antique types which had yielded place to the more perfect direct current machines. However, the currents used outside the dynamo, although direct, were, of course, the result of rectifying, by means of a commutator, the alternating currents produced in the armature by its own revolutions. All dynamos, therefore, produce alternating currents in the first instance, and in the same way all motors, before they will work at all, must be fed with alternating currents, whether a commutator is introduced to produce these alternations or not. The action of all machines used for the production of currents depends on the properties of magnetic change discovered by Faraday. The currents induced depend on the rate at which the magnetism varies, and alter in direction as it increases or diminishes. The magnetism cannot always be changing in the same direction, so that the currents induced must be alternating. Nearly all the useful appliances of magnetism result not so much from magnetism itself as from the alternation of it. This is the case, for instance, in telegraphy and telephony, in which we are always using varying or alternate current. If I pass an alternate current through one of the coils of this transformer we hear it singing. The current in the coil induces magnetism in the iron, and this changes in direction every time the current alternates. The magnetism acts on the windings of the coil, causing attractions which vary in amount with the strength of current; and it also causes in the iron itself stresses and strains which alter it every reversal of current. Vibrations are therefore set up which give rise to a note of a pitch corresponding with the frequency of the current. If due to any irregularities in driving or want of symmetry in the dynamo, the strength or frequency of the current is subject to variation, the note given out by the transformer will indicate this by altering its strength and pitch. The consequence is that the sound given out is very similar to the hum of the engine and dynamo. The transformer acts like a telephone; and, indeed, in principle a telephone is nothing more.

The first difficulty in connection with alternating currents is to settle how to measure them. They are continually varying, and therefore cannot be said to have any value in particular. If I pass the varying current produced by this commutator through an incandescent lamp you notice that when I turn the handle slowly the lamp varies in brightness as the strength of the current changes. If, however, I turn the handle quickly so as to produce twenty or more alternations per second the lamp burns quite steadily. The strength of the direct current which would make the lamp burn equally well is said to be the mean value of the alternating current used. This definition seems simple enough, but it defines the value of a current with reference to its heating effect only. It is soon realised that the importance of an alternating current depends chiefly on its magnetic influences, and not to any great extent on its heating effect. With steady currents the two are proportional, and each, therefore, is a measure of the other. Partly due to this cause, and partly due to the false notion that the current carries energy along with it, we are liable to confuse the heating effect of a current, which represents waste energy, with the useful energy of the current, which has no necessary connection with it, and in consequence some of the properties of alternating currents seem at first surprising. The efficiency and life of lamps seem to depend merely on the mean heating effect, for, as far as we know, they are the same for direct and alternating currents in spite of the fact that with the latter the maximum value of the current is far in excess of the mean value. With most of the practical applications of alternate currents, however, we have to bear in mind not only the strength of the currents, but also their frequency and magnetic surroundings. The currents and potentials are continually rising and falling in value. They are really waves, and have all the properties of waves.

Now one of the chief peculiarities about waves is that they do not add together in the same way that numbers do. They add together like forces. We all know that if two forces, each of one pound, are acting on a body, the effect is not the same as that of two pounds, unless the two forces act in the same direction. According to the angle between the forces the force equivalent to the two may vary from two pounds to nothing. If two men are pulling at the same rope in order to ring a church bell, it is necessary for them to pull together, or one will tend to stop the bell while the other is trying to ring it. In the same way two waves flowing to the same point will add to each other's effect if their rising and falling occur at the same time, but otherwise they will interfere and diminish each other's effect so that the resultant disturbance may be less than that which either would have caused separately. It does not, therefore, follow that two alternating currents flowing into the same wire will produce a current whose strength is the sum of the strengths of the two components, and, as Lord Rayleigh* has pointed out, if a current branches into two parts by means of two parallel circuits it may happen that each of the branch currents is greater than the original current.

I have bere the primary and secondary circuits of a Mordey transformer connected in parallel in such a way that if steady currents were flowing the coils would magnetise the iron in the same direction. In the main circuit, and also in each of the branch

594

circuits, a Bernstein lamp is placed. When I close the circuit you notice one lamp is much brighter than the others, and the brightest lamp is in the branch circuit, not in the main; if I now disconnect one of the branch circuits, the current diminishes to practically nothing, although the potential on the remaining coil actually increases. Shunting one coil with the other therefore not only increases the main current but also that in the part shunted. These effects of course do not occur with steady currents.

A somewhat similar experiment is due to Mr. Blakesley. His branch circuits consist, one of a resistance possessing self-induction, and the other of a condenser. By suitably choosing the capacity of the condenser it is possible to increase the current through the self-induction branch, and make it exceed the current in the main circuit. Mr. Blakesley calls his arrangement a condenser transformer, and it seems to have important practical bearings.

The following experiment is due to Mr. E. W. Smith of the Central Institution :-It is analogous to Lord Rayleigh's potentials being dealt with instead of currents. Here is a coil having a fairly large amount of self-induction in series with an inductionless resistance. Here are two similar lamps of large resistance shunted, one to the inductive and the other to the non-inductive resistance. I pass the alternating current through the arrangement, and adjust the resistance till the lamps are equally bright. Each lamp now measures the difference of potential of the points to which it is shunted. I now remove the wire which connects the junction of the two lamps with the junction of the inductive and non-inductive portions. You notice that each lamp diminishes in brightness, showing that the whole potential difference is less than the sum of the two halves. By making the shunt connection again each lamp brightens up, although Mr, Smith's experiments have shown, and theory confirms the fact, that the main current from the dynamo is diminished by so doing. By making the shunt connection we necessarily diminish the resistance, although the potentials appear to increase and the main current to diminish, quite the opposite of what would occur with steady

currents.

I have extended this experiment by forming a Wheatstone's bridge, two opposite arms of which consist of inductive resistances, the remaining arms being non-inductive. To each corner of the bridge I have attached a flexible lead coming to these lamps. The two wires attached to the corners of the bridge connected with the dynamo I have labelled red, and the remaining two, joining the parts of the bridge usually attached to the galvanometer, are labelled white. I connect the red wires to the terminals of the two lamps, the junction of which I connect successively with the white wires, adjusting in each case the corresponding non-inductive resistance till the lamps are equally bright. Each time I make connection with the white wire the lamps brighten as before. From analogy with steady currents we should now expect the bridge to be balanced, since the potential difference between either red and either white wire is the same. This, however, is not at all the case, for if I join the white wires to the extremities of the two lamps we notice they burn almost as brightly as when joined to the red wires connected directly with the dynamo. Theory indicates that if the impedance of the inductive arm were large, compared with its resistance, the potential between the white wires would be exactly equal to the potential between the red ones, and that in any case, if the bridge is balanced in the way described, there will be a difference in phase between the two potentials corresponding with a quarter of a period, so that one potential difference will reach its maximum when the other is at zero.

Now this is exactly the difference in phase required to drive a Tesla motor. I have here a small anchor ring of iron wound with coils in four quadrants. The coils in opposite quadrants are connected in series, so that a steady current flowing through either pair will cause a north and south pole in the adjacent quadrants. If, now, alternating currents, differing in phase by a quarter of a period, are sent through the two coils, each pole will move from one quadrant to the next every quarter of a period, so that the polarity will revolve round the ring with the same frequency as that of the alternating current. There is an iron disc free to revolve about the axis of the ring, and when I connect the red wires with one pair of coils, and the white wires with the other, you see the disc spins round at a great velocity, and thus forms a Tesla motor. There is, however, this peculiarity about it, that only one alternating current is used. The disadvantage of a Tesla motor is that it requires two alternating currents fixed in phase with reference to each other, so that it is necessary to have a special dynamo to produce the currents, and also to have at least three leads instead of two; here, however, is a method of making any alternate current work a Tesla motor. Mr. Blakesley* has, I find, already suggested his condenser transformer for the same purpose. The method I have suggested is not economical, but it can be improved by having the arms of the bridge of high resistance of impedance, and having two opposite quadrants of the Tesla field magnets wound with many turns of fine wire, instead of a few turns of thick wire. Moreover, if condensers of suitable capacity are substituted for the non-inductive arms of the bridge, the waste will be smaller, and the amplitude of the potential between the white wires will actually be greater than that between the red ones attached to the dynamo. At all events, there seems to be fair ground for supposing that some such arrangement can

* See the discussion on Mr. Kapp's paper on "Alternate Current Machinery." Proc. Inst. Civil Eng., February, 1889.

[NOVEMBER 22, 1839

be found by means of which a Tesla motor can be economia worked off any alternating current.

Striking effects of interference are obtained by putting s whose impedance is large compared with its resistance, in with a condenser of suitable capacity. If an alternating me is passed through such an arrangement, and measurem potential are made with a quadrant electrometer used cally, the potentials at the terminals of the coil or condenser each found to far exceed the potential at the ends of the or tion. Theory indicates that under the most favourable coact the two former are equal to each other, and the ratio of either the latter is then approximately equal to the ratio of the ing dance of the coil to its resistance, when this ratio is fairly lare

Thus, with the secondary of an induction coil having a run ance of 6,000 ohms, and co-efficient of self-induction of 50 quadr or secohms, and with a condenser of 0:05 microfarads cape calculation shows that the most favourable frequency of care to employ would be 98 periods per second, and that the poten on the coil and condenser would then be each about five time potentials on the two in series. In the confirmation of thi actual experiment I have had the advantage of the assistan Messrs. Monckton, Simon, and Taylor, of the Central Instit The field magnets of an alternator were excited with suit: currents, so as to produce at varying speeds of the dynam alternating potential of about 30 volts. In the annexed tablet results obtained are recorded. The number of periods per seal corresponding with the speed of the dynamo is indicated in th first column: the second column gives the ratio of the potent on the induction coil to that of the dynamo, and, of cours equal to the square root of the ratio of the corresponding de tions: the third column gives the ratio of the potential & condenser to that of the dynamo: the last column gives the of these two ratios, which, but for interference, would alway unity :

From these numbers it is evident that the potentials on the vo and condenser will be equal when the frequency is less than 1 periods per second, and that the sum of the two potentials will greater than 8.52 times the potential of the dynamo. When it considered that the self-induction of the coil, which had an i core, was measured, not with rapidly alternating currente, a with a single impulsive change of current, the agreement betwee the theory and experiment is quite satisfactory. but altbong theory so perfectly accounts for the effects, it is nevertheless prising that a difference of potential can be divided into two par each of which is so much greater than itself. Of course, if accumulators are connected up in series with 19 others, and e opposition the potential on the whole is two volts, while tho the parts are 40 and 38 respectively, this tends to prove, is practically true, that the alternating potentials are in oppos phase; but the peculiarity with alternating currents is that potentials of the two parts may be exactly equal, while that of whole is neither the sum of the two nor the zero difference. What is really happening in these cases of interference is le trated by an experiment on pulsations which I am able to pert by means of an ingeniously contrived commutator kindly lent by Mr. H. B. Bourne. Alternate bars of the commutator are onnected together and to the two ends of a battery of cells. There a two brushes, one fixed and the other movable, so that as the o mutator revolves one brush may be made to move over the ber more rapidly than the other. Each of these brushes is connect with the middle of the battery through the primary of a traze former. As the commutator revolves an alternating current c off from each brush. The period will be the same if the bre are both fixed, and the phase may be altered by moving one br with reference to the other. If one brush revolves slowly the t alternating currents are of slightly different period. The secondaries of the transformers are connected in series with th selves and with an incandescent lamp. The brightness of t lamp measures the sum of the two currents induced in the se daries by the alternating currents in the primaries. If currents coincide in phase the lamp burns brightly, while *** phase of the currents is opposite, as I can arrange by suitsty fixing the movable brush, the lamp is extinguished. If I move the movable brush slowly, the phase of the currents is tinually altering, and you see the lamp slowly pulsating in brigh ness. Although the two alternating currents induced in the s daries are always of the same strength, yet their sum varies fre zero to double the value of each, according to the phase of one respect to the other.

After all, however, the most extraordinary property of alte nating currents is that which has been longest known, viz, the tendency to transfer themseves from one circuit to another which they have apparently no connection. The appearance" these induced currents is accompanied, not by a decrease, but h an increase of the primary. The primary and secondary curre increase together. The explanation is that the currents are nearly opposite phase, and one current is neutralising the ma

tising effect of the other. The magnetism caused by alternating rrents always tends to a minimum, and the currents have to range themselves so that their joint magnetising effect may be small as possible. This tendency is very marked at high speeds, d the compensation is almost perfect. The little magnetism reining is, however, very important, because of its extremely pid rate of variation. The induced electromotive forces depend this rate of variation and not on the maximum amount of magtism. Thus in transformers there is a strong tendency for the imary and secondary currents to be in opposite phase. This is the explanation of a simple but important experiment e to Mr. Mordey, and the fact was proved by a large number of periments made by Messrs. C. G. Lamb and E. W. Smith at this llege some time ago.*

nes.

The strengths of the currents in the coils also arrange themIves to be nearly in inverse proportion to the number of turns, for is is the condition under which the magnetising effects should be ual. There is also a tendency for the magnetism to alter itself the simplest way possible, and this is according to the law of The secondary currents, therefore, tend to follow the law sines, because they exactly follow the variations of the magtism. The primary current will also follow the law of sines if Le magnetism is proportional to the current, but if saturation is proached, calculations which I have made from experimental ta show that the primary current may depart very much from a mple sine wave, as will also be the case if the electromotive force ting on the primary is itself irregular.

If

The tendency of magnetic change to a minimum is exemplified the action of choking coils, and in the heating of iron cores. opposite current can be induced in neighbouring circuits or odies so as to cancel the magnetising effect, the primary current allowed to flow, but otherwise the reluctance of the magnetism change suddenly will prevent the current rising to any magitude.

The same tendency occurs within the wire itself, for the adjacent ortions of the current tend to flow in opposite directions. The endency to reverse currents is strongest in the centre of the wire, nd consequently the current density is less there than near the urface. The resistance of the conductor is increased by this, and he alteration is very important when the wires are thick and the Iternations of the current are very frequent, as, for instance, in the nick wire circuit of electric welders. Thick leads are, therefore, ot well suited to alternating currents, but, on the other hand, hey are rarely necessary, for by means of transformers large mounts of energy can be efficiently transmitted immense disances by means of inexpensive thin wires.

It is not, however; only in engineering practice that alternate urrents have become of great importance. Within the last year r so the theory of electricity has been advanced tremendously by he study of alternating currents. We have seen that with rapid lternations the currents are determined chiefly by the magnetic hanges which are going on, and that they arrange themselves as far s possible to neutralise each others magnetic effect without much pparent regard to the electromotive forces acting on the resistnces in circuit. This tends to show that the most important part of an electric current is not in the wire itself, but in the egion outside. It has been, by considering the changes going on in the medium outside the wire, that Hertz has been able to xperimentally prove the existence of effects which have hitherto only had a mathematical basis. If a current is reversed in direcion, the lines of force surrounding it are also reversed. Maxwell's heory, however, states that they do not reverse instantly. The ines of force near the wire reverse before the others. There is a certain velocity at which the reversal of the lines travels, and this velocity, according to theory, should be about the same as the velocity of light. That this is actually the case is one of the things which Hertz has lately shown. In order to do so, he has made use of rapidly alternating currents. He has also employed a detector, whose great delicacy is due to the principle of resonance, which may be illustrated by an experiment of Prof. Ayrton's which I have arranged. An alternating current is passing along this stretched wire. When I hold a magnet near, the wire is pulled aside, due to the mutual action of the current and the magnet's lines of force. Every time the current reverses, the direction of the pull on the wire reverses, so that the wire is put into a state of vibration. The loudness of the sound, however, depends on the length of the stretched portion of the wire. There is one length which will give the best effect, and this happens when the wire is tuned to give out a note of the same pitch as that corresponding with the frequency of the alternating current. The current, in any case, forces the wire to give out a particular note; but if the wire naturally gives out that note, the sound produced is much greater. The interference of potentials occurring when an induction coil is placed in series with a condenser, is another instance of resonance, for the condition that the potential on the coil should be greatest compared with the whole potential acting on coil and condenser, can also be shown to be the condition that the natural period of oscillatory discharge of the condenser into the coil coincides with the period of the alternating current. It has been by using the principle of resonance that Hertz has been able to detect, in the medium outside the wire, cases of interference with magnetic reversals exactly similar

See discussion on Mr. Kapp's paper on "Alternate_Current Transformers," Journal Society Telegraph Engineers, February 23rd, 1888; see also a note of Profs. Ayrton and Perry, on "The Lag in Transformers," in the Electrician for March 16th, 1888.

to those I have shown you with alternating currents and potentials. His work has opened up an endless field of discovery, and these results have been brought about by making use of the peculiarities of alternating currents.

THE PROPOSED ELECTRIC CITY RAILWAY. OPPOSITION OF THE SEWERS COMMISSION.

ON Tuesday, at the meeting of the City Commissioners of Sewers at the Guildhall (Mr. GEORGE MANNERS in the chair), a letter was read from Messrs. Ashurst, Morris, Crisp & Co., the solicitors to the Bill for the proposed Central London Railway. The Bill provides for making a western terminus of the railway at Queen's Road, Bayswater, and for carrying the line along the Bayswater Road, Oxford Street, Holborn, Newgate Street, Cheapside and King William Street, making a junction with the City and Southwark subway, near Arthur Street West. There will be stations in the vicinity of the Marble Arch, Holborn Circus, the General Post Office and the Royal Exchange. The line is intended to be both lighted and worked by electricity. The letter from Messrs. Ashurst & Co. asked for instructions as to posting street notices regarding the proposed railway.

Mr. Wood moved, "That the Commissioners of Sewers do take steps to oppose the proposed Bill for the construction of the railway."

The CLERK stated that the only notice he had received was a communication asking how notices were to be posted.

Mr. WooD thought this an indication of how the promoters of this railway proposed dealing with the citizens. On Saturday his attention was directed to the fact that there were hanging to the lamp posts along Cheapside notices of an intention to apply to Parliament for the construction of a central London railway. He was referred by the company's solicitor to advertisements which were about to appear, and he found the clerk of the Commission had not received one of the notices which had been hanging on the lamp posts under their control. He did not hesitate to say that the project was one of the most momentous character. The railway proposed to pass from Marble Arch, down Oxford Street, It would Holborn, Newgate Street, Cheapside and Poultry. dislocate the traffic through the whole line of those thoroughfares, and inflict untold loss upon the traders. They remembered what they had suffered during the construction of the Metropolitan and District Railways, when whole thoroughfares were enclosed by hoardings, hundreds of carts were engaged removing the soil, the foundations of houses were insecure, and traders were grievously injured. The proposed electric railway would be a still more serious affair. The company proposed to obtain for nothing the whole of the ground under the roadway, which was public property, and to protect themselves against giving compensation to those whose interests might be damaged. The only advantage they offered the public was to travel through their stinking hole at the peril of their lives and certain injury to their health. (Laughter.) The scheme was a great Stock Exchange gamble the traders and citizens were to be the markers in the game, and poor shareholders would suffer irretrievable loss. He hoped the Commission would leave no stone unturned to defeat this most mischievous of projects.

Mr. J. C. BELL said he would second the resolution if the mover would amend it and refer the matter to committee. They could hardly imagine the chaos which would prevail, and possibly total ruin would ensue, to the traders along the line of route.

Mr. Wood consented to alter his resolution as suggested. Mr. PRICE thought the scheme of this electric railway was altogether premature. They should, first of all, ascertain what powers the company were seeking to obtain. By December 15th notices would have to be served on all interested, and afterwards the company would have to lodge their plans. Then they would be able to judge fairly about the matter. He did not suppose they would cut and cover as in Cannon Street, but let houses down in their route, which was mischievous enough

The CLERK stated that the company had taken it upon themselves to put the notices on the lamp posts. The Commission had never advised them what to do.

Alderman Sir W. LAWRENCE considered this a most important matter and one that required most careful and serious consideration. He would support the suggestion that the matter go to the Streets Committee for consideration and report. It was a subject that might well be discussed at the wardmotes on St. Thomas's Day. It had numerous bearings and wide issues. If such a railway would be beneficial to the City, then, after due consideration, they should support it. If, on the contrary, they should come to the conclusion that such a thing should not be allowed-as he believed they would-then they could make their opposition all the more powerfully felt when it was known that they had He thoroughly threshed out the subject in all its bearings. thought Mr. Wood was entitled to their thanks for making known the course of procedure.

Mr. DEPUTY WALTER thought the officers of the Commission ought to have torn the placards down.

Mr. SLY contended that at present the Commission were not in a position to understand the matter, and they ought not to take action before they were in possession of the facts.

Ultimately the court referred the matter to the Streets Committee.

596

INNOCENTS ABROAD.

DURING & discussion at a recent meeting of the American Institute of Electrical Engineers on Mr. Lockwood's paper," Electrical Notes of a Transatlantic Trip," an English electrician who is well known to the readers of the ELECTRICAL REVIEW, relieved his high tension feelings as follows:

Mr. G. L. ADDENBROOKE: I should be only too glad to say anything that I can, premising my remarks with the statement that I have been away from England very nearly a year, chiefly in Australia, and that I came here to find out what they have been doing in England. I rather came here to hear the latest news than to be able to say anything myself. It is a great pleasure to have heard Mr. Lockwood speak so appreciatively of the overhead work in England. We have felt satisfied, ourselves, that our overhead work has had a good many defects in it, but we look in England a great deal to people in America, and Mr. Lockwood having such thorough experience, and speaking so well of what we have accomplished, it gives us a great deal of gratification, especially as I happen to have been connected with the work in various capacities myself, both telephonic and electric lighting. In referring to overhead electric light work I am speaking rather of the past than of the future, because I think you are aware the commission appointed by the Board of Trade which has lately gone into the whole matter, has formed a set of regulations under which the whole of the electric lighting in London is to be placed underNo further overhead wires are ground as soon as possible. allowed to be placed, except such as may be agreed upon between the inspectors of the various companies, and the central station companies in London are now very hard at work laying down mains. However, there is no doubt a good deal of overhead work will be required for various purposes, and as you have so much overhead work here perhaps it might be worth while to explain our practice. First of all, we have not been allowed to plant posts in the streets at all, except in country roads. Within the boundaries of towns it is an absolute rule that no posts can be fixed in the streets. If we want posts we must put them in people's back gardens and in vacant lots, &c. Of course, this has necessitated that the majority of posts be placed on the tops of the houses. In foreign towns they have also had to go on the tops of the houses very largely. They have adopted one construction, we have adopted another. On the Continent most of the roofs have a very steep slope, and are tiled so that it is quite impossible to walk on them, and, of course, people do not put up stronger roofs than they can help--only strong enough to support the tiles and stand the wind, but not strong enough to support telephone posts. On the Continent, they use two long pieces of timber and form what they call a horse. That consists of a number of uprights and a lot of cross frames. I think you have some of them here. Nearly the whole of the work is done in that way, and I may mention that I happened to be with one of your countrymen, Mr. Wells, in Antwerp, and he also told me that any stray cats the linemen found there were always put in their tool bag and were eaten at home afterwards. In England we went to work in quite a different way. As Mr. Lockwood said, it is not unusual in London, at any rate, in overhead work on houses, to have wires arranged horizontally.

As a rule, there is but a single span. We have, first of all, what we call a chair. That is an iron casting weighing from 50 to 60 lbs., that goes on the top of the roof. From this rises a wrought iron tubular pole. Those tubes are carefully made to specification; they are about 3 inches internal diameter. It is usual to put up a pole of not less than 18 feet, but they range as high as 30. In the case of a pole 30 feet high, it is usual to have two or three poles, one inside the other, each pole having a collar and a bolt going through. These poles are simply stayed to the brick work. Heavy spikes are driven in the brick work. It is rather an agonising process for the house as you may imagine, but still somehow men have a way of doing it, and they drive spikes 8 inches long into the brick work. It is wonderful how the brick work stands it. I must say that I have seen some very large cracks occasionally. The wall itself will split out in the plaster occasionally. Each pole will have at least four of those stays under ordinary circumstances, and then, of course, it has to be stayed in accordance with the rules. When I came to America and saw the mass of wires running in all directions, it reminded me of what we call the early days of telephones in London, and we had so many faults with wires then that I could not understand how things worked here. So I looked about me and I find, apparently, the difference is that we think nothing of a span of 120 yards. Sometimes in telephone work we go 200 yards, and 150 yards is considered very little for a span of wires. Of course, in running wires that distance there is a very considerable amount of saving, and in a wind they are liable to come in contact with each other, and they are also apt to get out of regulation-that is, wires put in when the weather is hot, and wires put in when it is cold, and brought into unison, will get out of unison occasionally. So that perhaps accounts for the reason why you are able to run such a mass of wires about the streets and yet get along at all. When we had a rival in the Globe Telephone Company, we had a high old time in getting at each others "wayleaves." In putting up a pole 25 feet high and running wires from top to bottom, it is hard to get wires across in that vicinity. We went on for about two morths. If they were running a route here, we would run one across there. We got the two highest houses we could and blocked them, and they did the same to us. Of course it ended as most of those things do. The United Telephone Company bought

[NOVEMBER 22, 1889.

the other company out, and most of the wires were afterwards taken down. Then we come to another point, what we call "lead. ing in "-that is, taking the wire from the pole to the office of the subscriber. In England that is always done with gutta-percha covered wire. The people who began the telephone work in England were those who had had a little to do with telegrapha This wire costs about three or four pence a yard. It has a thick covering of first-class gutta-percha. Of course this insures inmunity from faults and leakage, and it is in some cases taped and in some cases braided. But if it is taped, it is very strongly taped, and the whole thing is what you call a very excellent job.

One very great reason why tramways perhaps have not made more advance in England is that posts are not allowed in the streets. Probably in the country districts they might be allowed, but without a lot of formalities, &c., before town councils, no leave to put up posts will be given. I think it is highly probable it will come, but still it will take time. On the other hand, notwith standing what has been said about electric railways here-I know perfectly well you have nearly a thousand miles in operation-I have just come from San Francisco; I stopped in San Francisco some days; I stopped at Denver and Salt Lake City and at Chicago and at Pittsburgh and at Philadelphia, and I have been here some days. At each of these places I have done all I could t see electric tramway work. I happened to see a car in the dis tance at Salt Lake City. They were putting up the wires in Pitts burgh. I was kindly shown a car running with accumulators here yesterday. I called on the Sprague Company and they said they had nothing which they could show within a hundred miles f New York, so that although you have a great deal, yet your country is so large, and the work so scattered about, that it d not show much, and I think, perhaps, the same applies to England. We certainly haven't got anything like that length of track, tat there are a lot of little tramways running about there which 1 think may be called to some extent the pioneers of tramway work For instance, there is the Blackpool tramway which has been running for several years. There is the Port Rush tramway in the north of Ireland, which I think was the first electrical tranway ever erected. There is a small tramway running along the Brighton Beach which has made things very popular. That bas been running six years. There are two or three companies in England operating experimental lines now in a small way, and certainly without going out of your way to see them you probably would not succeed in doing so. I had thought that perhaps Mr. Lockwood would have seen the new underground railway which runs from the Monument in the city to the Elephant and Castle. about three miles distant on the other side of the river. That is one of the most interesting engineering works which has lately been accomplished in England.

You all know something about the underground railway, which corresponds to your overhead railway here. Your elevated railway is certainly very efficient and very cheap. Ours is very expensive and some people say very nasty, but it answers its purpose an you don't see anything of it. Well, the new underground ra way in London starts from the Monument and goes right under the bed of the river at about 20 feet depth, and so far under the foundations of any houses that it has not been found necessary t compensate the owners. It goes about 60 feet under the houses At the Monument there is a station with hydraulic lifts. I st not aware whether it is actually running or not, but it is nearly finished, if not quite so. At each station there is a series of lifts by which the passengers go down or come up. From these tw tunnels are driven through the ground starting away to the other end of the line. This railway is going to be operated by elec tricity. The firm of Mather & Platt, of Manchester, undertook furnish the whole of the electrical plant and run it for a term years at a price which I believe at least I take this statement in a the paper-was considerably less than what it would cost the underground companies to work their locomotives by steam, and as Mather & Platt are a very large concern-who, by the way make the Edison dynamos in England, as well as the Manchesterno doubt they are prepared to stand the racket if it does not s ceed. But I think that will be a very interesting application By the way, Edward Hopkinson is their electrician. He wa brother of John Hopkinson.

Passing on to electric lighting, beginning at the station, at the Grosvenor, we were working with 2,500 volts; and the dynas were so perfectly self-regulating, at any rate when I was the and with the load they had on them, that all regulating applian were practically unnecessary beyond a sensitive governor on the engine and perhaps an electric governor on the engine and se thing to keep the exciter in order. All you have got to do is to kep your dynamo turning round at the same rate. The circuits so large that the putting on of lights or taking them off practis made no difference, and we always arranged things in this way that we never allowed, if we could help it at any rate, any lang circuits to be run in public buildings or theatres, or anything that. That is to say, we always contrived that not more than or 60 lamps should be turned off at the same time. Of cour man going around a building could turn off four or five swit but while he was doing that the engine driver would have a cha to look around. The circuits were so large that 50 or 60 light t or off practically made no difference, and most of the regulat was simply done by the engine driver standing near his ea when the curve was going up like that. Of course that simp matters very much.

The overhead work is done on very much the same line as t phone work, only the poles are shorter, sometimes they arent more than 12 feet, but as a rule they run to 18 feet. Near t