frictional or hydro-electrical machine on an enormous scale? Is not the reason, too, that no discharges take place under certain conditions, while they are frequent under other conditions, merely that the resistance of the circuit in the one case is so great that no discharge can take place, while in the other it has been reduced to within such limits that a spark can pass at some point? Consider the conditions a little closer. When do lightning discharges usually occur? Is it not when the atmosphere is full of moisture, drawn from the ground below by the intense heat of summer? and does not the same cause tend to reduce the resistance in another way-viz., by lessening the distance between the clouds and the earth, the heavy mass of vapour tending to pull it down? Next consider what happens when a cloud becomes charged. The writer is afraid that, with all due respect to Dr. Lodge, he must leave the elastic bags to take care of themselves, and revert to the reasoning that is common in other branches of electrical science. If a cloud becomes charged then, work is done upon it. It is capable of doing work in return, and will do that work if favourable conditions arise. Further, if a cloud, or one part of a cloud, becomes charged, say positively, it is implied that a nega tive charge exists elsewhere. Would it not be better to put this fact in the practical form in which electrical engineers are accustomed to deal with phenomena comprising the creation or the expenditure of electrical energy, and say that an E.M.F. is created between certain parts of the cloud and other objects; probably other portions of its own mass being included in the phenomena. If the E.M.F. existing between a point in the cloud and any point in surrounding objects be sufficient to overcome the electrical resistance opposed to it, then a current passes, varying in form according to the conditions present; such, for instance, as the rate at which the opposing resistance is lowered, etc. Probably minute, harmless, possibly health-giving electric currents are always passing between cloud and cloud, and from individual clouds to the earth. But in order that a current shall pass, we know that the whole resistance of the circuit must be such as will allow of its passage, not that of one small portion. It is well known that a shock of high voltage may be taken from a frictional or induction machine without danger, where the same voltage applied to the body from a dynamo used for electric lighting would cause instant death. The explanation is, that though the resistance of the body is the same in the two cases, or nearly so, that of the other portions of the circuit-in particular the internal resistance of the machine itself-is enormously greater in the one case than in the other, so great, in fact, as to absorb or use up a large portion of the E.M.F. generated before any current reaches the external circuit. Electrical engineers know whatit means to have a dynamo or a battery whose internal resistance is out of proportion to that of the apparatus to be worked. Take, for instance, a battery of 10 cells, each having an internal resistance of 10 ohms, while that of the line and apparatus outside is only one ohm. As we know, we practically get no current from such a combination; and we should get none from it if we had 100 or 1,000 similar cells. And so it is with the Holtz machine, and with the thundercloud.

But what is the circuit which governs the discharge of the thundercloud? It is assumed that the cloud acts only as one plate of a condenser or Leyden jar, the earth forming the other; that the cloud, once charged, may be looked upon as cut off-just as one may charge a Leyden jar and have done with it. Obviously, this is an incorrect description; and it is only fair to Dr. Lodge to mention that in his experiments he does not appear to take this view. It is evident, of course, that a charged cloud fills the same, or nearly the same, position with regard to surrounding objects that a frictional machine does. It is a generator, and at the same time it forms one side of the condenser, of which the earth and other clouds form the other. But it must not be forgotten that while there is an inductive connection-if it may be so termed between the cloud and surrounding bodies, there is also a conductive connection, and that the office of the inductive connection is only to determine the positions of strains, or of E.M.F's. Consider, again, what happens when a charged cloud sails over a particular portion of the earth's surface. Probably, during its motion, its charge is being increased

by friction with the atmosphere. We know, also, that assuming one extremity of the cloud to be charged positively, the earth and other objects near will be charged negatively. At any rate, there is an E.M.F. existent between them, similar to that existing, say, between the terminals of a dynamo; and if we examine surrounding objects, we shall find that they display characteristics which we associate with a charge of a certain name, opposite in character to that of the inducing body, the cloud. But, assuming this to be correct, how did the charge reach the objects named? We know, for instance, that the nearer objects will be more highly charged than those more remote, and we know that this charge means-unfortunately this is where we want a little more light. At any rate, we do know that the induced charge, whether positive or negative, has only been allowed by conduction from surrounding objects. That is to say, when, in obedience to the inducing force exercised by a highly-charged thundercloud, the top of a factory chimney, say, becomes positively electrified, or there appears a difference of potential between it and not only the cloud, but surrounding bodies on its own side of the condenser dielectric, this state has been arrived at by means of electric currents passing from these surrounding bodies, and possibly from the cloud itself, to the chimney-top. When also, owing either to the departure of the cloud, or to its whole or partial discharge, the strain is relieved at that particular point-in other words, the difference of potential is lowered, and a redistribution takes place this also will be by means of currents of electricity, as we understand them. Further, when a discharge between a thundercloud and an object attached to earth takes place, be that object a mill chimney, a Royal palace, an oak, or an animal, the discharge, be it harmless or disastrous, must be by means of one or more electric currents, taking the term in the sense in which we now understand it.

The point whether a Leyden jar discharge, or a lightning discharge, be by continuous or oscillatory currents, in the writer's opinion hardly affects the question. If the discharge is oscillatory, it will be so because under certain conditions, an opposing E.M.F. is created in the process of first discharge, which in turn delivers its current along the path or paths open to it. Nor can the question whether a conductor of large sectional area offers the resistance that Ohm's law would dictate, or offers a higher apparent resistance owing to induction within itself, affect the argument. It may at once be acknowledged that a copper rod, or rope, or tape may be considered for the purpose of the passage of an electric current through its mass, as composed of a bundle of rods of infinitely small sectional area, and it is obvious that if this is so, and there is no reason to question the premise, the current passing in each of these rods or wires acts inductively upon those passing in all the others, and in such a manner as will resist their passage; because, as we know, each current creates around it a series of circles of magnetisation within which the others would be enclosed, and these resent, so to speak, the entrance into them of another current creating magnetic fields of a similar name. Further, we know, by the laws of magneto-electric induction, that these effects, giving rise to apparent resistance, are proportional to the current strength, other things being the same. We know also that in all these cases the current strength depends upon the E.M.F. available, and inversely upon the resistance of the circuit. In other words, the whole thing depends upon the difference of potential between the cloud and the top of the conductor, and inversely upon the resistance of the path or paths chosen, nolens volens by the discharging current, so that we come right back to our initial question-What is the path of the discharging current and what part does "earth" play in the discharge? The apparent increase of the ohmic resist ance of any lightning conductor, owing to magneto-electric induction within itself, would really appear to be too small a matter, considering the magnitude of the figures involved, to have any serious bearing upon the question. Here it may be well to state another problem for solution. It is the problem of which the question, "What part does 'earth' play in a lightning discharge" forms a part. It is, what is necessary to protect buildings, electrical instruments, such as telephones and dynamos, or trees and

animals from being struck by dangerous lightning discharges. The answer is, in the writer's opinion, that the E.M.F. available for driving a current through the body to be protected must be reduced below the dangerous point, or below that at which either a dangerously powerful heating or shocking current, or a dangerously powerful spark, can be delivered through the circuit of which the body to be protected forms a part.

It is obvious that this end may be accomplished in two ways only-viz., by interposing in the circuit which it is designed to protect a high resistance, or by shunting the circuit by means of a conductor of such low resistance that the shunted current lowers the E.M.F. at the terminals of the body or instrument to be protected below the danger point. Possibly an example taken from practical electrical engineering work will make this clear.

Suppose that you have an electrical pumping plant which is being worked at an E.M.F. in the mains of 300 volts or thereabouts, and you wish to run incandescent lamps on the same circuit; you have only 100-volt lamps, and the problem is therefore to use these lamps without overheating them. The problem, of course, is a very simple one. You either use three of the lamps in series, or where you cannot use three lamps together within any reasonable distance, you introduce an artificial resistance between one main and one terminal of the lamp. In either case you use up the surplus 200 volts by introducing the additional resistance, reducing the E.M.F. at the terminals of the lamp to the figure you require, 100 volts, thereby only allowing the proper current to pass through it. But you might also have accomplished the object by causing a large current to pass through the mains and through another branch circuit, the current passing being of sufficient magnitude to reduce the voltage at the terminals of the lamp to the same figure as before-viz., 100 volts-by reason of the charge made upon the initial E.M.F. present for the passage of this current through the mains, in opposition to their electrical resistance.

Take the resistance of the mains between the terminals of the dynamo and those of the motor at one ohm, and the normal working current as 20 amperes; the E.M.F. at the terminals of the dynamo being 320 volts, giving 300 volts at the terminals of the lamp. Now bridge across the mains at a point near where you require the lamp with a shunt, having a resistance of 1.5 ohms, which will allow of the passage of a current of 200 amperes. Making use of the usual formula E = CR, we find that the passage of this current through the mains absorbs 200 volts, and the E.M.F. at the point where the shunt is connected, while the shunt current is passing, will be only 100 volts.

The above is, of course, only a hypothetical case, though it might occur under such conditions as the waste of power in the mains being of no consideration even when of the large magnitude described, and the shunt circuit might be represented by a motor using that current. Such a case might also arise from defective engineering. The example, whether hypothetical or practical illustrates the two methods that rule for protecting life and property from the current of a high-tension supply, or from lightning. The first method, the introduction of an artificial resist ance into the circuit, is that usually adopted by attendants upon high-tension dynamos, when they place a piece of dry wood near the machine to stand upon while they are oiling, etc., when the machine is running. The second plan is the one that has hitherto been adopted almost universally in the matter of lightning conductors, but which, as the writer understands the matter, Dr. Oliver Lodge says is wrong. The first plan is also obviously one that could be adopted in case of being caught in a thunderstorm. If one knew where to stand upon a piece of close rock, which itself piece of close rock, which itself stood upon ground that did not hold moisture readily, one would have accomplished the object sought after-viz., by introducing an artificial resistance into the circuit, lessened the chances of a dangerous current passing through one.

It will be evident, however, that whichever plan is chosen the return path is a matter of considerable importance. In the example that has been chosen the return path is a cable or other conductor; and the question will arise here, Is a return path necessary in the case of lightning? The writer maintains that lightning requires a

path for redistribution of its charge, for the expenditure of its stored energy, just as much as either an electric light supply system requires one, or a frictional electrical machine does. But consider, first, what would be the effect of having a return path of high resistance in the case where you propose to take off a powerful shunt current for any purpose. Your high-resistance return path will prevent your doing it, because you will be unable to get the necessary strength of current through. It must be remembered that in dealing with protection from lightning the two classes of cases must be kept quite distinct. If an object is already protected, by the fact that from its position a high resistance is offered to any current that can be sent through it from a thundercloud, it requires no other. But, on the other hand, if the object to be protected stands in such a position that the natural resistance offered to the current that would be sent through it from a thundercloud is not sufficient to protect it under all circumstances, and it becomes necessary to protect it by the other plan, then the high resistance of the return path is an obstacle in the way of accomplishing this. And it is here that the necessity for good, very good earth, appears to the writer to come in.

What is the return path, or, if it be preferred, the path for redistribution of the charge on a thundercloud? The charge would, as already stated, probably be formed in the process of the formation of the cloud itself, and by friction with the atmosphere as it sailed over the earth. Whence did this charge come? Evidently principally from the moisture in the surrounding atmosphere, a little from the air itself. But the fact of a charge of electricity having been taken from the atmosphere between the cloud and the earth would cause a current from the earth, and from buildings, animals, chimneys, etc., producing the phenomena we know to exist-viz., the charge of an opposite name on those portions of the earth's surface, and the objects upon it, immediately under the cloud. When a redistribution takes place it can only be by means of currents passing through the conductors present. The method of redistribution will, of course, depend upon the conditions ruling at the time. Thus the effect of the discharge of one cloud might be neutralised by the presence of another, and the discharge of the cloud might take place not to any object upon the earth, but to another cloud, in which case quite a different set of conditions would be set up. Again, the cloud might not discharge at all in the neighbourhood where it was generated, and where it acquired the major portion of its charge.

In any case, however, whatever the cause of the redistribution, it could only take place by conduction. Now, consider, if this true, what it means. It does not mean that only metals, or the inside of chimney shafts, or wet trees, or animals will take part in the redistribution, but that these and every other body which lies in the path of the E.M.F. present will take its proportion of current according to Ohm's law-i.e., in inverse proportion to their resistances. It should be mentioned here that there will probably be electromagnetic induction between different portions of the discharging or redistributing current, when passing through earth, rocks, trees, or any other body, just as there will be between the different portions passing through a lightning rod. There will also be electrolysis set up at different points, both giving rise to counter E.M.F.'s, and the current passing in any path will be ruled by the final E.M.F. available for overcoming the resistance of that path, after allowing for these counter E.M.F.'s, just as the current passing in an electric motor would.

Now it will be evident that as the mass of the earth's crust takes part very largely in this redistribution or discharge, whichever it is called, the current passing in any part of that crust will depend upon two things onlythe formation of the crust at that particular point, and the surface contact between the principal conductor contained in it and the conductor leading to the ground.

Take, for instance, a broad, deep river, such as the Thames or the Mersey; the resistance offered by the river to the discharging or redistributing current must be small, provided the contact made between it and, say, the end of a conductor leading to it is large. On the other hand, the resistance offered by a hard, impervious rock will be light,

But, as is well known, if the contact with the river is very small, the resistance offered to the current may be high; while even in the case of a hard rock, if we could obtain a large enough surface contact, the resistance might be reduced to moderate dimensions.

But how does this affect the question of the lightning discharge? In the writer's opinion the question is affected by these matters, because in all cases of discharge or redistribution, it is along these paths that the current which carries out the redistribution must flow.

There is a difference of potential between one end of the cloud and one part of the earth, but there is also, by reason of that difference of potential, a further tension between the same part of the earth and neighbouring portions, and no matter how the result may come-either by sparking from the cloud to some object on the earth's surface, by sparking from cloud to cloud, by silent discharge between cloud and surrounding objects, or by the cloud moving on whenever a redistribution does take place it necessitates currents passing between the parts of the earth, or the objects on it, that are at different potentials, and these currents must pass through the earth's crust, the objects on it, and through the surrounding atmosphere in accordance with the laws already stated.

Now examine the case of a lightning conductor attached to a high building or to a mill chimney. What position does it occupy with reference to the charged cloud overhead? It is perhaps as well to explode the old idea that the conductor is able to attract all the charge to itself. The lightning-rod forms merely one of many paths open to the discharging or redistributing current. Each of the chimneys. of the building, with their soot linings, forms another part. The stone or brickwork of which the building or chimney is composed forms other paths, mainly on account of the moisture held in them.

If the lightning conductor is able to protect the building to which it is attached, it will be because the additional path formed by it for the discharging current has reduced the E.M.F. available below the point at which it can do other mischief.

But if it is to do that, obviously it must be arranged to carry the largest possible current away. Obviously, also, the only way in which this can be accomplished is by making the conductor form a portion of a path of low resistance; and how is this to be done except by connecting it by means of a large surface contact with the mass of the best conductors to be found in the earth's crust where the conductor joints it-in other words, by making good earth as electrical engineers understand the term.

The lightning current will not mind ploughing up a few yards of earth when it reaches ground, but there is no reason that it should be allowed to do so if it can be avoided, as it can by making a good earth connection.

What

A good earth would, of course, mean, if available, the bed of a river, wide and deep, connection being made to the water by means of a large metal plate. But, it is replied, if good earth, as you call it, will do the trick, why are buildings struck where the conductors have good earth? Why is a poor sheep struck in the open, standing upon wet ground? Surely he is making good earth. about side flashes also? Where does good earth come in there? The answer is, and it had better be faced at once, that unless the number of conductors is much multiplied, in the case of large buildings, each conductor making good earth, and, if possible, a separate earth, unless the bed of a large river is available, it is impossible to absolutely ensure protection from lightning. But while it is impossible to ensure absolute protection from lightning, just as it is impossible to ensure immunity from many other things, the one thing that will tend, and the only thing that will tend to protect from lightning is the multiplication before described, all the conductors being well earthed.

It is obvious, of course, that where good earth is obtainable fewer conductors are necessary than where it is not. The reason why this is the only plan available is that which has been already mentioned-viz., that the conductor only forms one path of many open to the discharging current, and that it only protects if it is able to reduce the E.M.F. present between the cloud, or the conductor when struck, and surrounding objects below danger point. In the case

of a large square building, it might very possibly happen that portions of its roof would be at different potentials, from the very fact of the existence of a conductor on one side; and though one side might be efficiently protected by the conductor placed there, there might be a dangerous E.M.F. still existing after discharge between another part of the cloud and some other part of the building. The remedy is obviously, multiply conductors and earth them all separately. The same reasoning applies to side flashes. They are due to the existence of an E.M.F. between the conductor while carrying out its office of discharging or redistributing, and the object to which the flash passes, which the conductor has not been able to kill. It should be noted, however, that side flashes cannot take place except to objects which form part of a circuit of such resistance that a current can pass through this path, including the air space over which the flash passes. Gas brackets and pipes are the most usual recipients of side flashes, the reason being that they, being in connection with the large mass of main pipes lying in the ground, forming good earth, affords such a path as has been described. The remedy is, as before, multiply the lightning conductors, and apply the high resistance method to the gas-pipes and other possible recipients. Place them as far from the path of discharge as you can.

The case of animals and trees being struck in the open field arises from the fact that there is no discharging path near, and therefore a dangerous E.M.F. is present, the actual path of the discharge being determined by special conditions in each case.

The remedy would be here, as in other cases, to fix a number of conductors about a field where animals grazed during thunder weather, always getting as good earth as possible. A similar plan would probably protect valuable plantations of forest trees.

In conclusion, the writer would point, in confirmation of his views, to the comparative immunity of towns from the effect of lightning discharges, and he attributes this immunity to the fact that so many paths are open for the discharge of the thundercloud. Most of them have a high. resistance, and do not make good earth, but their infinite multiplication gives the same result, even to the good earth, in another form. Suppose, for instance, the resistance of the column of smoky hot air, soot-lined chimney, fire-grate, and foundation together amount to 1,000 ohms, a thousand such paths will bring the resistance to only one ohm; while in the case of a very large city, the combined resistance of all the paths open to the discharging current would be very small indeed.

The writer would also point to the fact that though lightning has frequently been seen in the workings of a mine, and has often pulled down colliery chimneys, and done damage at the pit bottom, no damage has ever been done by it in the mine itself, the coal, rails, etc., acting as conductors to distribute the charge, and the damage done at the pit bottom being due to the sudden break from a conductor of low resistance to one of high resistance, without good surface contact-without, in fact, a good connection to earth.

The writer has not touched upon the static side of the question, but it is obvious that most of the remarks given above apply equally, whether the matter be looked at from the electrostatic or electro-dynamic point of view. Each conductor, each body that will or does conduct, not only does so, but it dissipates a portion of the charge from the electrostatic capacity of the condenser or condensers, of which it forms a part; and this is surely an argument for getting the conducting surface to which the discharging current is conveyed as large as possible. That is getting good earth.

It should perhaps be noted that the office of good "earth" would be very well filled by the congregation together of a number of large masses of metal, in more or less good connection, electrically speaking, such as a large town built entirely of iron-a thing which may perhaps one day come to pass. Failing this, however, our next best substitute is the earth's crust, solely on account of its large proportions, and this is only available where we can get good connection to the principal conductor in it, the moisture that is always present.

THE B.A. MEETING.

Electricians of all grades and of all opinions have never been wanting in praise of the good work done by the British Association on electrical measurements. Its resolutions have had a world-wide effect. All countries have accepted them, and have had little or nothing to say against the work. There is no doubt but that the B.A. committee was formed at an opportune moment and did yeoman service for the cause. Chaos gave place to order. Some of the younger spirits of the Association, seeing what great good arose from the committee on measurements, have an idea that a discussion on units— notation and nomenclature-may be of some service. This new departure in discussion between two sections puts us in mind of a musical ride by the Guards. It is very showy, very entertaining, but of no real value. We have attended several of these discussions, but do not remember that any tangible result was ever obtained. There is no doubt that some settled system of units is required, instead of every individual author propounding units and names for himself. There is, again, a good feature in the endeavour to perpetuate the name of a man renowned in science by giving his name to some common unit, but this system may be carried to excess. Are we so conceited as to imagine that Science is going to stand still after our day? What about the men of the It certainly seems so. future? We are acting as if our conclusions were infallible; whereas half a century hence may show them to have been as far from the truth as the conclusions of the Greeks in astronomy. Discuss units by all means; but not through a formal or informal meeting of sections, but by means of a well-organised committee.

CITY AND SOUTH LONDON RAILWAY.

"I hope that the future profits of the line will go on steadily increasing, and that it will not be so very long before I may have the pleasure of standing here and feeling that we have earned a substantial dividend. But that rests with the future, and I do not like to prophesy on these points." Thus the chairman of the City and South London Railway Company at the half-yearly meeting held on Tuesday last. Everything was going on very well. The Board could affirm that their system of electric locomotion would work, and could go even further, and say that it had worked satisfactorily. Butwould it pay? Well, the future must answer that question. They hoped and believed it would. At present, however, the company have only just managed to pay the interest on their debenbalance of £555. And unless the weekly receipts, tures, £4,137, and to carry forward a small which we have published regularly in our City Notes, show some signs of expansion, it does not look as if a much better financial statement awaits the shareholders next winter. The Board are doing their best to fill up the trains during the middle of

the day. At first, as it At first, as it will be remembered, a uniform fare of 2d. all the way was charged. But it was soon found that though this did well enough for the through traffic, which tested the capacity of the railway to its uttermost in the morning and evening, it rather interfered with the intermediate station to station traffic. In order, therefore, to fill their trains during the middle of the day, the company introduced penny fares at certain stations and at stated times. The result was satisfactory, and the receipts at these stations increased some 50 per cent. The question of carrying this system of reduced fares still further is being carefully considered by the directors. Naturally they do not like giving up the uniform system, which is convenient and cheap to work; but the encouragement of a 50 per cent. rise will probably go a long way to helping the board to give up their pet idea. There are some pleasant features in the chairman's speech, however. It is satisfactory tobe able to carry 23 millions of people without an accident. True, this was qualified the other day by a fatal mishap in connection with one of the big lifts. But as the individual who met his death" acted in violation of the company's by-laws and in direct defiance of its officers," the chairman is fairly entitled to his expression of satisfaction; though, as we have pointed out in a recent issue, the company would do well to see to the closing of the doors of its lifts before they are set in motion. Then the working expenses are being cut down; the staff have been educated in their duties; the lighting of the trains has been improved; and fresh departures in the way of perfection are being considered The Board have had to give up their Islington extension project, a fact which will afford satisfaction to those shareholders who want to see the old line pay before a new one is built.

LIGHTNING AND CONDUCTORS.

It is not always wise to prohibit publicity to opinions not in accordance with those held by the majority. Mr. S. F. Walker throws down the gauntlet to Dr. Lodge, but Mr. Walker may rest assured that Dr. Lodge will not enter into any controversy upon the subject. Dr. Lodge has promulgated heterodox views in regard to protection from lightning, and has, we believe, taken the majority with him in most of the opinions he has advanced. There are points, however, in which Dr. Lodge is just as likely to be wrong as he is to be right. So long as Mr. Walker holds to the view that lightning, or any other form of electricity, acts in accordance with Ohm's law, and traverses the circuit of least resistance, he is upon pretty safe ground, and we should hesitate to believe Dr. Lodge objects to this, as Mr. Walker seems to think. There is absolutely no reason to be advanced why lightning should act in any other direction than the circuit of least resistance though it would be impossible in the present state of our knowledge to trace the circuit. Much of what Dr. Lodge has

advanced points to the old view that electricity is an entity, but no doubt theories are about as near to the actual facts as were the theories of our ancestors in regard to heat to those of the present day. However, our readers will judge for themselves how far Mr. Walker has weakened Dr. Lodge's contention. After all, what is good earth? Is it one link in the circuit? What are the varying conditions which at one time makes a part of the earth's surface a good conductor at another time not so good? Is moisture the sole ingredient in the "good" or "bad"? We always took it to be admitted that pure water was not so good a conductor as those who go in for moist earth would have us believe. Is good earth, then, determined by what the water holds in suspension? what constitutes the best earth, and how would Mr. Walker obtain it?

If so,

UNDERGROUND LIGHTING MAINS IN PARIS.*

BY E. DIEUDONNÉ.

In accordance with the conditions laid down by the specification which regulates this matter, all electric condiffers according to the companies to whom the concession ductors are underground. The method of laying them for so doing is granted. One principle common to all is that they must be laid in trenches under the footways at a suitable distance from the houses, and that where the roadways are crossed vaulted subways large enough to admit men must be provided. The Place Clichy sector, however, is not provided with these latter. As is known, the area of the city has been split up into a certain and extending to the circumference bounded by the city number of zones, dividing the central portions or arteries, wall. These geographical divisions, called sectors from the distant resemblance their configuration bears to the geometrical figure of this name, have been handed over under the conditions and clauses of the specification to different companies under concessions. We shall only deal with those (in alphabetical order) which have carried out work (the others will appear in due time)—viz. :

(a) The Compagnie Parisienne d'air comprimé et d'electricité.

(b) The Société d'éclairage et de force par l'electricité. (c) The Société Edison.

(d) The Société du Secteur de la place Clichy.

(A) Parallel with these four groups is the city station. at the central markets.

The special precautions taken in the different methods of method of distribution adopted. We will make a few running mains are generally adjusted according to the digressions into this particular subject to determine its general characteristics, without unduly putting aside the subject of this article.

Compagnie d'air comprimé et d'electricité.

* From L'Electricien.