GENERAL VIEW OF A LABORATORY AT THE PARIS SCHOOL OF PHYSICS AND CHEMISTRY.GENERAL VIEW OF A LABORATORY AT THE PARIS SCHOOL OF PHYSICS AND CHEMISTRY.
The pupils occupy themselves regularly every day, during half the time spent at the school, with practical work in analytical and applied chemistry and physics and general chemistry. This practical work is a complement to the various lectures, and has reference to what has been taught therein. Once or twice per week the pupils spend three hours in a shop devoted to wood and metal working, and learn how to turn, forge, file, adjust, etc.
The school's cabinets are now provided with the best instruments for study, and are daily becoming richer therein. The chemical laboratories are none the less remarkably organized. In the accompanying cut we give a view of one of these—the one that is under the direction of Mr. Schultzenberger, professor of chemistry and director of the new school. Each pupil has his own place in front of a large table provided with a stand whereon he may arrange all the products that he has to employ. Beneath the work-table he has at his disposal a closet in which to place his apparatus after he is through using them. Each pupil has in front of him a water-faucet, which is fixed to a vertical column and placed over a sink. Alongside of this faucet there is a double gas burner, which may be connected with furnaces and heating apparatus by means of rubber tubing. A special hall, with draught and ventilation, is set apart for precipitations by sulphureted hydrogen and the preparation of chlorine and other ill-smelling and deleterious gases. The great amount of light and space provided secure the best of conditions of hygiene to this fine and vast laboratory, where young people have all the necessary requisites for becoming true chemists.—La Nature.
Within the last few years a singular interest has arisen in the subject of dust, smoke, and fog, and several scientific researches into the nature and properties of these phenomena have been recently conducted. It so happened that at the time I received a request from the secretary of this society to lecture here this afternoon I was in the middle of a research connected with dust, which I had been carrying on for some months in conjunction with Mr. J.W. Clark, Demonstrator of Physics in University College, Liverpool, and which had led us to some interesting results. It struck me that possibly some sort of account of this investigation might not be unacceptable to a learned body such as this, and accordingly I telegraphed off to Mr. Moss the title of this afternoon's lecture. But now that the time has come for me to approach the subject before you, I find myself conscious of some misgivings, and the misgivings are founded upon this ground: that the subject is not one that lends itself easily to experimental demonstration before an audience. Many of the experiments can only be made on a small scale, and require to be watched closely. However, by help of diagrams and by not confining myself too closely to our special investigation, but dealing somewhat with the wider subject of dust in general, I may hope to render myself and my subject intelligible if not very entertaining.
First of all, I draw no distinction between "dust" and "smoke." It would be possible to draw such a distinction, but it would hardly be in accordance with usage. Dust might be defined as smoke which had settled, and the term smoke applied to solid particles still suspended in the air. But at present the term "smoke" is applied to solid particles produced by combustion only, and "dust" to particles owing their floating existence to some other cause. This is evidently an unessential distinction, and for the present I shall use either term without distinction, meaning by dust or smoke, solid particles floating in the air. Then "fog"; this differs from smoke only in the fact that the particles are liquid instead of solid. And the three terms dust, smoke, and fog, come to much the same thing, only that the latter term is applied when the suspended particles are liquid. I do not think, however, that we usually apply the term "fog" when the liquid particles are pure water; we call it then mostly either mist or cloud. The name "fog," at any rate in towns, carries with it the idea of a hideous, greasy compound, consisting of smoke and mist and sulphur and filth, as unlike the mists on a Highland mountain as a country meadow is unlike a city slum. Nevertheless, the finest cloud or mist that ever existed consists simply of little globules of water suspended in air, and thus for our present purpose differs in no important respect from fog, dust, and smoke. A cloud or mist is, in fact, fine water-dust. Rain is coarse water-dust formed by the aggregation of smaller globules, and varying in fineness from the Scotch mist to the tropical deluge. It has often been asked how it is that clouds and mists are able to float about when water is so much heavier (800 times heavier) than air. The answer to this is easy. It depends on the resistance or viscosity of fluids, and on the smallness of the particles concerned. Bodies falling far through fluids acquire a "terminal velocity," at which they are in stable equilibrium—their weight being exactly equal to the resistance—and this terminal velocity is greater for large particles than for small; consequently we have all sorts of rain velocity, depending on the size of the drops; and large particles of dust settle more quickly than small. Cloud-spherules are falling therefore, but falling very slowly.
To recognize the presence of dust in air there are two principal tests; the first is, the obvious one of looking at it with plenty of light, the way one is accustomed to look for anything else; the other is a method of Mr. John Aitken's, viz., to observe the condensation of water vapor.
Take these in order. When a sunbeam enters a darkened room through a chink, it is commonly said to be rendered visible by the motes or dust particles dancing in it; but of course really it is not the motes which make the sunbeam visible, but the sunbeam the motes. A dust particle is illuminated like any other solid screen, and is able to send a sufficient fraction of light to our eyes to render itself visible. If there are no such particles in the beam—nothing but clear, invisible air—then of course nothing is seen, and the beam plunges on its way quite invisible to us unless we place our eyes in its course. In other words, to be visible, light must enter the eye. (A concentrated beam was passed through an empty tube, and then ordinary air let in.)
The other test, that of Mr. Aitken, depends on the condensation of steam. When a jet of steam finds itself in dusty air, it condenses around each dust particle as a nucleus, and forms the white visible cloud popularly called steam. In the absence of nuclei Mr. Aitken has shown that the steam cannot condense until it is highly supersaturated, and that when it does it condenses straight into rain—that is, into large drops which fall. The condensation of steam is a more delicate test for dust than is a beam of light. A curious illustration of the action of nuclei in condensing moisture has just occurred to me, in the experiment—well known to children—of writing on a reasonably clean window-pane with, say, a blunt wooden point, and then breathing on the glass; the condensation of the breath renders the writing legible. No doubt the nuclei are partially wiped away by the writing, and the moisture will condense into larger drops with less light-scattering power along the written lines than over the general surface of the pane where the nuclei are plentiful, and the drops therefore numerous and minute. Mr. Aitken points out that if the air were ever quite dustless, vapor could not condense, but the air would gradually get into a horribly supersaturated condition, soaking all our walls and clothes, dripping from every leaf, and penetrating everywhere, instead of falling in an honest shower, against which umbrellas and slate roofs are some protection. But let us understand what sort of dust it is which is necessary for this condensing process. It is not the dust and smoke of towns, it is not the dust of a country road; all such particles as these are gross and large compared with those which are able to act as condensers of moisture. The fine dust of Mr. Aitken exists everywhere, even in the upper regions of the atmosphere; many of its particles are of ultra-microscopic fineness, one of them must exist in every raindrop, nay, even in every spherule of a mist or cloud, but it is only occasionally that one can find them with the microscope. It is to such particles as these that we owe the blue of the sky, and yet they are sufficiently gross and tangible to be capable of being filtered out of the air by a packed mass of cotton-wool. Such dust as this, then, we need never be afraid of being without. Without it there could be no rain, and existence would be insupportable, perhaps impossible; but it is not manufactured in towns; the sea makes it; trees and wind make it; but the kind of dust made in towns rises only a few hundred yards or so into the atmosphere, floating as a canopy or pall over those unfortunate regions, and sinks and settles most of it as soon as the air is quiet, but scarcely any of it ever rises into the upper regions of the atmosphere at all.
Dust, then, being so universally prevalent, what do I mean by dust-free spaces? How are such things possible? And where are they to be found? In 1870 Dr. Tyndall was examining dusty air by means of a beam of light in which a spirit-lamp happened to be burning, when he noticed that from the flame there poured up torrents of apparently thick black smoke. He could not think the flame was really smoky, but to make sure he tried, first a Bunsen gas flame and then a hydrogen flame. They all showed the same effect, and smoke was out of the question. He then used a red-hot poker, a platinum wire ignited by an electric current, and ultimately a flask of hot water, and he found that from all warm bodies examined in dusty air by a beam of light the upstreaming convection currents were dark. Now, of course smoke would behave very differently. Dusty air itself is only a kind of smoke, and it looks bright, and the thicker the smoke the brighter it looks; the blackness is simply the utter absence of smoke; there is nothing at all for the light to illuminate, accordingly we have the blankness of sheer invisibility. Here is a flame burning under the beam, and, to show what real smoke looks like, I will burn also this spirit lamp filled with turpentine instead of alcohol.Whythe convention currents were free from dust was unknown; Tyndall thought the dust was burnt and consumed; Dr. Frankland thought it was simply evaporated.
In 1881 Lord Rayleigh took the matter up, not feeling satisfied with these explanations, and repeated the experiment very carefully. He noted several new points, and hit on the capital idea of seeing what a cold body did. From the cold body the descending current was just as dark and dust-free as from a warm body. Combustion and evaporation explanations suffered their death-blow. But he was unable to suggest any other explanation in their room, and so the phenomenon remained curious and unexplained.
In this state Mr. Clark and I took the matter up last summer, and critically examined all sorts of hypotheses that suggested themselves, Mr. Clark following up the phenomena experimentally with great ingenuity and perseverance. One hypothesis after another suggested itself, seemed hopeful for a time, but ultimately had to be discarded. Some died quickly, others lingered long. In the examination of one electrical hypothesis which suggested itself we came across various curious phenomena which we hope still to follow up.2It was some months before what we now believe to be the true explanation began to dawn upon us. Meanwhile we had acquired various new facts, and first and foremost we found that the dark plane rising from a warm body was only the upstreaming portion of a dust-freecoatperpetually being renewed on the surface of the body. Let me describe the appearance and mode of seeing it by help of a diagram. (For full description seePhilosophical Magazinefor March, 1884.)
Surrounding all bodies warmer than the air is a thin region free from dust, which shows itself as a dark space when examined by looking along a cylinder illuminated transversely, and with a dark background. At high temperatures the coat is thick; at very low temperatures it is absent, and dust then rapidly collects on the rod. On a warm surface only the heavy particles are able to settle—there is evidently some action tending to drive small bodies away. An excess of temperature of a degree or two is sufficient to establish this dust-free coat, and it is easy to see the dust-free plane rising from it. The appearances may also be examined by looking along a cylindertowardthe source of light, when the dust-free spaces will appear brighter than the rest. A rod of electric light carbon warmed and fixed horizontally across a bell-jar full of dense smoke is very suitable for this experiment, and by means of a lens the dust-free regions may be thus projected on to a screen. Diminished pressure makes the coat thicker. Increased pressure makes it thinner. In hydrogen it is thicker, and in carbonic acid thinner, than in air. We have also succeeded in observing it in liquids—for instance, in water holding fine rouge in suspension, the solid body being a metal steam tube. Quantitative determinations are now in progress.
Fig. 1 and Fig. 2
Fig. 1 shows the appearance when looking along a copper or carbon rod laterally illuminated; the paths of the dust particles are roughly indicated. Fig. 2 shows the coat on a semi-cylinder of sheet copper with the concave side turned toward the light.
It is difficult to give the full explanation of the dust free spaces in a few words, but we may say roughly that there is a molecular bombardment from all warm surfaces by means of which small suspended bodies get driven outward and kept away from the surface. It is a sort of differential bombardment of the gas molecules on the two faces of a dust particle somewhat analogous to the action on Mr. Crookes' radiometer vanes. Near cold surfaces the bombardment is very feeble, and if they are cold enough it appears to act toward the body, driving the dust inward—at any rate, there is no outward bombardment sufficient to keep the dust away, and bodies colder than the atmosphere surrounding them soon get dusty. Thus if I hold this piece of glass in a magnesium flame, or in a turpentine or camphor flame, it quickly gets covered with smoke—white in the one case, black in the other. I take two conical flasks with their surfaces blackened with camphor black, and filling one with ice, the other with boiling water, I cork them and put a bell jar over them, under which I burn some magnesium wire; in a quarter of an hour or so we find that the cold one is white and hoary, the hot one has only a few larger specks of dust on it, these being of such size that the bombardment was unable to sustain their weight, and they have settled by gravitation. We thus see that when the air in a room is warmer than the solids in it—as will be the case when stoves, gas-burners, etc., are used—things will get very dusty; whereas when walls and objects are warmer than the air—as will be the case in sunshine, or when open fireplaces are used, things will tend to keep themselves more free from dust. Mr. Aitken points out that soot in a chimney is an illustration of this kind of deposition of dust; and as another illustration it strikes me as just possible that the dirtiness of snow during a thaw may be partly due to the bombardment on to the cold surface of dust out of the warmer air above. Mr. Aitken has indeed suggested a sort of practical dust or smoke filter on this principle, passing air between two surfaces—one hot and one cold—so as to vigorously bombard the particles on to the cold surface and leave the air free.
But we have found another and apparently much more effectual mode of clearing air than this. We do it by discharging electricity into it. It is easily possible to electrify air by means of a point or flame, and an electrified body has this curious property, that the dust near it at once aggregates together into larger particles. It is not difficult to understand why this happens; each of the particles becomes polarized by induction, and they then cling together end to end, just like iron filings near a magnet. A feeble charge is often sufficient to start this coagulating action. And when the particles have grown into big ones, they easily and quickly fall. A stronger charge forcibly drives them on to all electrified surfaces, where they cling. A fine water fog in a bell jar, electrified, turns first into a coarse fog or Scotch mist, and then into rain. Smoke also has its particles coagulated, and a space can thus be cleared of it. I will illustrate this action by making some artificial fogs in a bell-jar furnished with a metal point. First burn some magnesium wire, electrify it by a few turns of this small Voss machine, and the smoke has become snow; the particles are elongated, and by pointing to the charged rod indicate the lines of electrostatic force very beautifully; electrify further, and the air is perfectly clear. Next burn turpentine, and electrify gently; the dense black smoke coagulates into black masses over an inch long; electrify further, and the glass is covered with soot, but the air is clear. Turpentine smoke acts very well, and can be tried on a larger scale; a room filled with turpentine smoke, so dense that a gas-light is invisible inside it, begins to clear in a minute or two after the machine begins to turn, and in a quarter of an hour one can go in and find the walls thickly covered with stringy blacks, notably on the gas-pipes and everything most easily charged by induction. Next fill a bell-jar full of steam, and electrify, paying attention to insulation of the supply point in this case. In a few seconds the air looks clear, and turning on a beam of light we see the globules of water dancing about, no longer fine and impalpable, but separately visible and rapidlyfalling. Finally, make a London fog by burning turpentine and sulphur, adding a little sulphuric acid, either directly as vapor or indirectly by a trace of nitric oxide, and then blowing in steam. Electrify, and it soon becomes clear, although it lakes a little longer than before; and on removing the bell-jar we find that even the smell of SO2has disappeared, and only a little vapor of turpentine remains. Similarly we can make a Widnes fog by sulphureted hydrogen, chlorine, sulphuric acid, and a little steam. Probably the steam assists the clearing when gases have to be dealt with. It may be possible to clear the air of tunnels by simply discharging electricity into the air—the electricity being supplied by Holtz machines, driven say by small turbines—a very handy form of power, difficult to get out of order. Or possibly some hydro-electric arrangement might be devised for the locomotive steam to do the work. I even hope to make some impression on a London fog, discharging from lightning conductors or captive balloons carrying flames, but it is premature to say anything about this matter yet. I have, however, cleared a room of smoke very quickly with a small hand machine.
It will naturally strike you how closely allied these phenomena must be to the fact of popular science that "thunder clears the air." Ozone is undoubtedly generated by the flashes, and may have a beneficial effect, but the dust-coagulating and dust-expelling power of the electricity has a much more rapid effect, though it may not act till the cloud is discharged. Consider a cloud electrified slightly; the mists and clouds in its vicinity begin to coagulate, and go on till large drops are formed, which may be held up by electrical action, the drops dancing from one cloud to another and thus forming the very dense thunder cloud. The coagulation of charged drops increases the potential, as Prof. Tait points out, until at length—flash—the cloud is discharged, and the large drops fall in a violent shower. Moreover, the rapid excursion to and fro of the drops may easily have caused them to evaporate so fast as to freeze, and hence we may get hail.
While the cloud was electrified, it acted inductively on the earth underneath, drawing up an opposite charge from all points, and thus electrifying the atmosphere. When the discharge occurs this atmospheric electrification engages with the earth, clearing the air between, and driving the dust and germs on to all exposed surfaces. In some such way also it may be that "thunder turns milk sour," and exerts other putrefactive influences on the bodies which receive the germs and dust from the air.
But we are now no longer on safe and thoroughly explored territory. I have allowed myself to found upon a basis of experimental fact, a superstructure of practical application to the explanation of the phenomena of nature and to the uses of man. The basis seems to me strong enough to bear most of the superstructure, but before being sure it will be necessary actually to put the methods into operation and to experiment on a very large scale. I hope to do this when I can get to a suitable place of operation. Liverpool fogs are poor affairs, and not worth clearing off. Manchester fogs are much better and more frequent, but there is nothing to beat the real article as found in London, and in London if possible I intend to rig up some large machines and to see what happens. The underground railway also offers its suffocating murkiness as a most tempting field for experiment, and I wish I were able already to tell you the actual result instead of being only in a position to indicate possibilities. Whether anything comes of it practically or not, it is an instructive example of how the smallest and most unpromising beginnings may, if only followed up long enough, lead to suggestions for large practical application. When we began the investigation into the dust-free spaces found above warm bodies, we were not only without expectation, but without hope or idea of any sort, that anything was likely to come of it; the phenomenon itself possessed its own interest and charm.
And so it must ever be. The devotee of pure science never has practical developments as his primary aim; often he not only does not know, but does not in the least care whether his researches will ever lead to any beneficial result. In some minds this passive ignoring of the practical goes so far as to become active repulsion; so that some singularly biased minds will not engage in anything which seems likely to lead to practical use. I regard this as an error, and as the sign of a warped judgment, for after all man is to us the most important part of nature; but the system works well nevertheless, and the division of labor accomplishes its object. One man investigates nature impelled simply by his own genius, and because he feels he cannot help it; it never occurs to him to give a reason for or to justify his pursuits. Another subsequently utilizes his results, and applies them to the benefit of the race. Meanwhile, however, it may happen that the yet unapplied and unfruitful results evoke a sneer, and the question: "Cui bono?" the only answer to which question seems to be: "No one is wise enough to tell beforehand what gigantic developments may not spring from the most insignificant fact."
[1]
Lecture to the Royal Dublin Society by Dr. Oliver J. Lodge, April 2, 1884.
Lecture to the Royal Dublin Society by Dr. Oliver J. Lodge, April 2, 1884.
[2]
For instance, the electric properties of crystals can be readily examined in illuminated dusty air; the dust grows on them in little bushes and marks out their poles and neutral regions, without any need for an electrometer. Magnesia smoke answers capitally.
For instance, the electric properties of crystals can be readily examined in illuminated dusty air; the dust grows on them in little bushes and marks out their poles and neutral regions, without any need for an electrometer. Magnesia smoke answers capitally.
For the last eighteen months a system has been in active operation in Belgium whereby the ordinary telegraph wires are used to convey telephonic communications at the same time that they are being employed in their ordinary work of transmitting telegraphic messages. This system, the invention of M. Van Rysselberghe, whose previous devices for diminishing the evil effects of induction in the telephone service will be remembered, has lately been described in theJournal Telegraphiqueof Berne, by M.J. Banneux of the Belgian Telegraph Department. Our information is derived from this article and from others by M. Hospitalier.
The method previously adopted by Van Rysselberghe, to prevent induction from taking place between the telegraph wires and those running parallel to them used for telephone work, was briefly as follows: The system of sending the dots and dashes of the code—usually done by depressing and raising a key which suddenly turns on the current and then suddenly turns it off—was modified so that the current should rise gradually and fall gradually in its strength by the introduction of suitable resistances. These were introduced into the circuit at the moment of closing or opening by a simple automatic arrangement worked exactly as before by a key. The result, of the gradual opening and gradual closing of the circuit was that the current attained its full strength gradually instead of suddenly, and died away also gradually. And as induction from one wire to another depends not on the strength of the current, but on the rate at which the strength changes, this very simple modification had the effect of suppressing induction. Later Van Rysselberghe changed these arrangements for the still simpler device of introducing permanently into the circuit either condensers or else electro-magnets having a high coefficient of self-induction. These, as is well known to all telegraphic engineers, retard the rise or fall of an electric current; they fulfill the conditions required for the working of Van Rysselberghe's method better than any other device.
Having got thus far in his devices for destroying induction from one line to another, Van Rysselberghe saw that, as an immediate consequence, it might be concluded that, if the telegraph currents were thus modified and graduated so that they produced no induction in a neighboring telephone line, they would produce no sound in the telephone if that instrument were itself joined up in the telegraph line. And such was found to be case. Why this is so will be more readily comprehended if it be remembered that a telephone is sensitive to the changes in the strength of the current if those changes occur with a frequency of some hundreds or in some cases thousands of timesper second. On the other hand, currents vibrating with such rapidity as this are utterly incompetent to affect the moving parts of telegraphic instruments, which cannot at the most be worked so as to give more than 200 to 800 separate signalsper minute.
Fig. 1Fig. 1
The simplest arrangement for carrying out this method is shown in Fig. 1, which illustrates the arrangements at one end of a line. M is the Morse key for sending messages, and is shown as in its position of rest for receiving. The currents arriving from the line pass first through a "graduating" electromagnet, E2, of about 500 ohms resistance, then through the key, thence through the electromagnet, R, of the receiving Morse instrument, and so to the earth. A condenser, C, of 2 microfarads capacity is also introduced between the key and earth. There is a second "graduating" electromagnet, E1, of 500 ohms resistance introduced between the sending battery, B, and the key. When the key, M, is depressed in order to send a signal, the current from the battery must charge the condenser, C, and must magnetize the cores of the two electromagnets, E1and E2, and is thereby retarded in rising to its full strength. Consequently no sound is heard in a telephone, T, inserted in the line-circuit. Neither the currents which start from one end nor those which start from the other will affect the telephones inserted in the line. And, if these currents do not affect telephones in the actual line, it is clear that they will not affect telephones in neighboring lines. Also the telephones so inserted in the main line might be used for speaking to one another, though the arrangement of the telephones in the same actual line would be inconvenient. Accordingly M. Van Rysselberghe has devised a further modification in which a separate branch taken from the telegraph line is made available for the telephone service. To understand this matter, one other fact must be explained. Telephonic conversation can be carried on, even though the actual metallic communication be severed by the insertion of a condenser. Indeed, in quite the early days of the Bell telephone, an operator in the States used a condenser in the telegraph line to enable him to talk through the wire. If a telephonic set at T1(Fig. 2) communicate through the line to a distant station, T2, through a condenser, C, of a capacity of half a microfarad, conversation is still perfectly audible, provided the telephonic system is one that acts by induction currents. And since in this case the interposition of the condenser prevents any continuous flow of current through the line, no perceptible weakening will be felt if a shunt S, of as high a resistance as 500 ohms and of great electromagnetic rigidity, that is to say, having a high coefficient of self-induction, be placed across the circuit from line to earth. In this, as well as in the other figures, the telephones indicated are of the Bell pattern, and if set up as shown in Fig. 2, without any battery, would be used both as transmitter and receiver on Bell's original plan.Fig. 2Fig. 2But as a matter of fact any ordinary telephone might be used. In practice the Bell telephone is not advantageous as a transmitter, and has been abandoned except for receiving; the Blake, Ader, or some other modification of the microphone being used in conjunction with a separate battery. To avoid complication in the drawings, however, the simplest case is taken. And it must be understood that instead of the single instrument shown at T1or T2, a complete set of telephonic instruments, including transmitter, battery, induction-coil, and receiver or receivers, may be substituted. And if a shunt, S, of 500 ohms placed across the circuit makes no difference to the talking in the telephones because of the interposition of the separating condenser, C, it will readily be understood that a telegraphic system properly "graduated," and having also a resistance of 500 ohms, will not affect the telephones if interposed in the place of S. This arrangement is shown in Fig. 3, where the "graduated" telegraph-set from Fig. 1 is intercalated into the telephonic system of Fig. 2, so that both work simultaneously, but independently, through a single line. The combined system at each end of the line will then consist of the telephone-set, T1, the telegraph instruments (comprising battery, B1, key, M1and Morse receiver, R1), the "graduating" electromagnets, E1, and E2, the "graduating" condenser, C1, and the "separating" condenser, C2. It was found by actual experiments that the same arrangement was good for lines varying from 28 to 200 miles in length. A single wire between Brussels, Ghent, and Ostend is now regularly employed for transmission by telegraph of the ordinary messages and of the telemeteorographic signals between the two observatories at those places, and by telephone of verbal simultaneous correspondence, for one of the Ghent newspapers. A still more interesting arrangement is possible, and is indicated in Fig. 4. Here a separating condenser is introduced at the intermediate station at Ghent between earth and the line, which is thereby cut into two independent sections for telephonic purposes, while remaining for telegraphic purposes a single undivided line between Brussels and Ostend. Brussels can telegraph to Ostend, or Ostend to Brussels, and at the same time the wire can be used to telephone between Ghent and Ostend, or between Ghent and Brussels, or both sections may be simultaneously used.
Fig. 3Fig. 3
Fig. 4Fig. 4
It would appear, then, that M. Van Rysselberghe has made an advance of very extraordinary merit in devising these combinations. We have seen in recent years how duplex telegraphy superseded single working, only to be in turn superseded by the quadruplex system. Multiplex telegraphy of various kinds has been actively pursued, but chiefly on the other side of the Atlantic rather than in this country, where our fast-speed automatic system has proved quite adequate hitherto. Whether we shall see the adoption in the United Kingdom of Van Rysselberghe's system is, however, by no means certain. The essence of it consists in retarding the telegraphic signals to a degree quite incompatible with the fast-speed automatic transmission of telegraphic messages in which our Post Office system excels. We are not likely to spoil our telegraphic system for the sake of simultaneous telephony, unless there is something to be gained of much greater advantage than as yet appears.—Nature.
For registering the height of the tide at every instant, hydrographic services generally adopt quite a simple marigraph. The apparatus consists in principle of a counterpoised float whose rising and falling motion, reduced to a tenth, by means of a system of toothed wheels, is transmitted to a pencil which moves in front of a vertical cylinder. This cylinder itself moves around its axis by means of a clockwork mechanism, and accomplishes one entire revolution every twenty-four hours. By this means is obtained a curve of the tide in which the times are taken for abscisses and the heights of the sea for ordinates. However little such marigraphs have had to be used, great defects have been recognized in them. When we come to change the sheet on the cylinder (and such change should be made at least once every fifteen days), there is an interruption in the curve. It is necessary, besides, to perform office work of the most detailed kind in order to refer to the same origin all these curves, which are intercrossed and often superposed in certain parts upon the original sheet. In order to render such a disentanglement possible, it is indispensable to mark by hand, at least once every twenty-four hours, upon each curve, the date of the day corresponding to it. It is equally useful to verify theexactness of the indications given by the apparatus by making readings several times a day on a scale of tides placed alongside of the float. Nine times out of ten the rise of the waves renders such readings very difficult and the control absolutely illusory.
All these conditions united, as well as others that we neglect in this brief discussion, necessitate a surveillance at every instant. The result is that these marigraphs must be installed in a special structure, very near the bank, so as to be reachable at all times, and that the indications that they give are always vitiated by error, since the operation is performed upon a level at which are exerted disturbing influences that are not found at a kilometer at sea. It were to be desired that the float could be isolated by placing it a certain distance from the shore, and transmit its indications, by meant of a play of currents, to a registering apparatus situated uponterra firma.
In the course of one of his lectures published in the December number (1883) of theElektrotechnische Zeitschrift, Mr. Von Hefner-Alteneck tells us that such a desideratum has been supplied by the firm of Siemens & Halske. This marigraph, constructed on an order of the German Admiralty, gives the level of the sea every ten minutes with an approximation of 0.12 per cent., and that too for a difference of 8 meters between the highest and lowest sea. The apparatus consists, as we said above, of a float and registering device, connected with each other by means of a cable. This latter is formed of three ordinary conductors covered with gutta percha and surrounded with a leaden sheath, which latter is itself protected against accident by means of a strong covering of iron wire and hemp. The return is effected through the earth. We shall enter into details concerning each of these two apparatus in-succession, by beginning with the float, of which Fig. 1 gives a general view, and Fig. 2 a diagrammatic sketch. The float moves in a cast iron cylinder, having at its lower part a large number of apertures of small diameter, so that the motion of the waves does not perceptibly influence the level of the water in the interior of the cylinder. It is attached to a copper ribbon, B, whose other extremity is fixed to the drum, T. The ribbon winds around the latter in the rising motion of the float, owing to a spiral spring arranged so as to act upon the drum. The tension of this spring goes on increasing in measure as the float descends.
Fig. 1Fig.1.—FLOAT OF SIEMENS AND HALSKE'S MARIGRAPH.
This difference in tension is utilized for balancing at every instant the weight of the ribbon unwound, and thus causing the float to immerse itself in the water to a constant degree. The ribbon, B, is provided throughout its length with equidistant apertures that exactly correspond to tappets that project from the circumference of the wheel, R. When the float moves its position, the wheel, R, begins to turn and carries along in doing so the pinion,w, which revolves over the toothed wheels, s1, s2, and s3. The thickness of w is equal to that of the three wheels, s1, s2, and s3, and a special spring secures at every instant an intimate contact between the pinion and the said wheels. These latter are insulated from each other and from the axle upon which they are keyed, and communicate, each of them, with conductors, I., II., and III. They are so formed and mounted that, in each of them, the tooth in one corresponds to the interspace in the two others. As a result of this, in the motion of the pinion,w, the latter is never in contact with but one of the three wheels, s1, s2, and s3.
Fig. 2.Fig.2.
If we add that the lines, I., II., and III. are united at the shore station with one of the poles of a pile whose other pole is connected with the earth, and that w communicates with the earth through the intermedium of R, and the body of the apparatus, it is easy to see that in a vertical motion of the float in one direction we shall have currents succeeding each other in the order I., II., III., I., II., etc., while the order will become III., II., I., III., II., etc., if the direction of the float's motion happen to change.
Fig. 3.Fig.3.
Fig. 4.Fig.4.
In order to understand how a variation in currents of this kind can be applied in general for producing a rotary motion in the two directions, it will only be necessary to refer to Figs. 3 and 4. The conductors, L1, L2, and L3communicate with the bobbins of three electromagnets, E1, E2, and E3, whose poles are bent at right angles to the circumference of the wheel, R. There is never but one pole opposite a tooth. The distance between two consecutive poles must be equal to a multiple of the pitch increased (Fig. 3) or diminished (Fig. 4) by one-third thereof. It will be seen upon a simple inspection of the figures that R will revolve in the direction of the hands of a watch when the currents follow the order L1, L2, L3, etc., in the case shown in Fig. 3, while in the case shown in Fig. 4 the rotary motion will be in the contrary direction for this same order of currents. But, in both cases, and this is the important point, the direction of rotation changes when the order in the succession of currents; is inverted. Fig. 6 gives a perspective view of the registering apparatus, and Fig. 5 represents it in diagram. It will be at once seen that, the toothed wheel,r, is reduced to its simplest expression, since it consists of two teeth only. The electro-magnets are arranged at an angle of 120°, and for achange of current the wheel,r, describes an angle of 60°, that is to say, a sixth of a circumference. The motion of r is transmitted, by means of the pinion,d, and the wheel,e, to the wheel, T. For a one-meter variation in level the wheel, T, makes one complete revolution. It is divided into 100 equal parts, and each arc therefore corresponds to a difference of one centimeter in the level, and carries, engraved in projection, the corresponding number. As a consequence, there is upon the entire circumference a series of numbers from to 99. The axle upon which the wheel, T, is keyed is prolonged, on the side oppositee, by a threaded part,a, which actuates a stylet,g. This latter is held above by a rod, I, which is connected with a fork movable around a vertical axis, shown in Fig. 6. The rectilinear motion of g is 5 mm. for a variation of one meter in level. Its total travel is consequently 40 mm. The sheet of paper upon which the indications are taken, and which is shown of actual size in Fig. 7, winds around the drum, P, and receives its motion from the cylinder, W. This sheet is covered throughout its length with fine prepared paper that permits of taking the imprints by impression.
Fig. 5.Fig.5.
Fig. 6.Fig.6—RECEIVER OF SIEMENS AND HALSKE'S MARIGRAPH.
This stated, the play of the apparatus may be easily understood. Every ten minutes a regulating clock closes the circuit of the local pile, B2, and establishes a contact at C. The electro-magnet, E4, attracts its armature, and thus acts upon the lever,h, which presses the sheet of paper against the stylet in front that serves to mark the level of the lowest waters, and against the stylet,g, and the wheels, T and Z. In falling back, the lever,h, causes the advance, by one notch, of the ratchet wheel that is mounted at the extremity of the cylinder W, and thus displaces the sheet of paper a distance of 5 mm. The wheel, Z, carries engraved in projection upon its circumference the hours in Roman figures, and moves forward one division every 60 minutes. The motion of this wheel is likewise controlled by the cylinder, W.
It will be seen upon referring to Fig. 7, that there is obtained a very sharp curve marked by points. We have a general view on considering the curve itself, and the height in meters is read directly. The fractions of a meter, as well as the times, are in the margin. Thus, at the point,a, the apparatus gives at 3 o'clock and 20 minutes a height of tide of 4.28 m. above the level of the lowest water.
Fig. 7.Fig.7.
This apparatus might possibly operate well, and yet not be in accord with the real indications of the float, so it has been judged necessary to add to it the following control.
Every time the float reaches 3 meters above the level of the lowest tide, the circuit of one of the lines that is open at this moment (that of line I, for example) closes at C (Fig. 2), into this new circuit there is interposed a considerable resistance, W, so that the energy of the current is weakened to such a point that it in nowise influences the normal travel of the wheel,r. At the shore station, there is placed in deviation a galvanoscope, K, whose needle is deflected. It suffices, then, to take datum points upon the registering apparatus, upon the wheel, T, and the screw,a, in such a way as to ascertain the moment at which the stylet,g, is going to mark 3 meters. At this moment the circuit of the galvanoscope, K, is closed, and we ascertain whether there is a deviation of the needle.
As the sea generally rises to the height of 3 meters twice a day, it is possible to control the apparatus twice a day, and this is fully sufficient.
It always belongs to practice to judge of an invention. Mr. Von Hefner-Alteneck tells us that two of these apparatus have been set up—one of them a year ago in the port of Kiel, and the other more recently at the Isle of Wangeroog in the North Sea—and that both have behaved excellently since the very first day of their installation. We shall add nothing to this, since it is evidently the best eulogium that can be accorded them.—La Lumiere Electrique.
In recent times considerable attention has been paid to the subject of laying telegraph cables underground, and various methods have been devised. In some cases the cables have been covered with an armor of iron, and in others they have been inclosed in cast-iron pipes. For telephonic service they are generally inclosed in leaden tubes. What this external envelope shall be that is to protect the wires from injury is a question of the highest importance, since not only the subject of protection is concerned, but also that of cost. It is therefore interesting to note the efforts that are being made in this line of electric industry.
Fig. 1. Section of the Pipe Open.Fig.1. Section of the Pipe Open.
Fig. 2. Section of the Pipe Closed.Fig.2. Section of the Pipe Closed.
Messrs. Delune & Co. have recently taken out a patent for an arrangement consisting of pipes made of beton. The annexed cuts, borrowed fromL'Electricite, represent this new system. The pipes, which are provided with a longitudinal opening, are placed end to end and coupled with a cement sleeve. The cables are put in place by simply unwinding them as the work proceeds, and thus all that traction is done away with that they are submitted to when cast iron pipes are used. When once the cables are in place the longitudinal opening is stopped up with cement mortar, and in this way a very tight conduit is obtained whose hardness increases with time. The value of the system therefore depends, as in all cement work, on the care with which the manufacturing is done.
Experiments have been made with the system at Toulouse, by the Minister of Post Offices and Telegraphs, and at Lyons, by the General Society of Telephones. Here, as with all similar questions, no opinion can be pronounced until after a prolonged experience. But we cannot help setting forth the advantages that the system offers. These are, in the first place, a saving of about 50 per cent. over iron pipe, and in the second, a better insulation, and consequently a better protection of the currents against all kinds of disturbance, since a non-conducting mass of cement is here substituted for metal.
"There is nothing new but what has been forgotten," said Marie Antoinette to her milliner, Mdlle. Bertin, and what is true of fashion is also somewhat so of science. Shoeing restive horses by the aid of electricity is not new, experiments thereon having been performed as long ago as 1879 by Mr. Defoy, who operated with a small magneto machine.
But the two photographs reproduced in Figs. 1 and 2 have appeared to us curious enough to be submitted to our readers, as illustrating Mr. Defoy's method of operating with an unruly animal.