Chapter 6

(2.) When two or more vibrating bodies are immersed in a fluid, they set up around them fields of vibration, and act and react upon one another in a manner closely analogous to the action and reaction of magnets upon one another, producing the phenomena of attraction and repulsion. In this respect, however, the analogy appears to be inverse, repulsion being produced where, from the magnetic analogy, one would expect to find attraction, and _vice versa_.

(3.) If a neutral body, that is to say a body having no vibration of its own, be immersed in the fluid and within the field of vibration, phenomena are produced exactly analogous to the magnetic and diamagnetic phenomena produced by the action of a magnet upon soft iron or bismuth, its apparently magnetic or diamagnetic properties being determined by the specific gravity of the neutral body as compared to that of the medium in which it is immersed. If the neutral body be lighter than the medium, it exhibits the magnetic induction of iron with respect to polarity, but is nevertheless repelled; while if it be heavier than the medium, its direction is similar to that of diamagnetic bodies such as bismuth, but on the other hand exhibits the phenomena of attraction.

In this way Professor Bjerknes has been able to reproduce analogues of all the phenomena of magnetism and diamagnetism, those phenomena which may be classed as effects of induction being directly reproduced, while those which may be classed as effects of mechanical action, and resulting in change of place, are analogous inversely. This fact has been so much misunderstood both in this country and on the Continent that it will be well, before describing the experiments, to enter more fully into an explanation of these most interesting and instructive phenomena.

For the sake of clearness we will speak of magnetic induction as that property of a magnet by which it is surrounded by a field of force, and by which pieces of iron, within that field, are converted into magnets, and pieces of bismuth into diamagnets, and we will speak of magnetic action as the property of a magnet by which it attracts or repels another magnet, or by which it attacks or repels a piece of iron or bismuth magnetized by magnetic induction.

The corresponding hydrodynamic phenomena may be regarded in a similar manner; thus, when a vibrating or pulsating body immersed in a liquid surrounds itself with a field of vibrations, or communicates vibrations to other immersed bodies within that vibratory field, the phenomena so produced may be looked upon as phenomena of hydrodynamic induction, while on the other hand, when a vibrating or pulsating body attracts or repels another pulsating or vibratory body (whether such vibrations be produced by outside mechanical agency or by hydrodynamical induction), then the phenomena so produced are those of hydrodynamical action, and it is in this way that we shall treat the phenomena throughout this article, using the words _induction_ and _direct action_ in these somewhat restricted meanings.

In the hydrodynamical experiments of Professor Bjerknes all the phenomena of magnetic induction can be reproduced directly and perfectly, but the phenomena of magnetic action are not so exactly reproduced, that is to say, they are subject to a sort of inversion. Thus when two bodies are pulsating together and in the same phase (i. e., both expanding and both contracting at the same time), they mutually attract each other: but if they are pulsating in opposite phases, repulsion is the result. From this one experiment taken by itself we might be led to infer that bodies pulsating in similar phases are the hydrodynamic analogues of magnets having their opposite poles presented to one another, and that bodies pulsating in opposite phases are analogous to a presentation of similar magnetic poles; but it will be seen at once that this cannot be the case if three magnetic poles or three pulsating bodies be considered instead of only two. It is clear, on the one hand, that three similar magnet poles will all repel one another, while, on the other, of three pulsating bodies, two of them must always attract one another, while a third would be repelled; and, moreover, two similarly pulsating bodies set up around them the same lines of force as two similar magnetic poles, and two oppositely pulsating bodies produce lines of force identically the same as those set up by two magnets of opposite polarity. Thus it will be seen that there is a break in the analogy between the hydrodynamical and the magnetic phenomena (if a uniform inversion of the effects can be called a break, for it is, as far as Professor Bjerknes' experiments go, without an exception); and if by any means this inversion could be reinverted, all the phenomena of magnetism and diamagnetism could be exactly reproduced by hydrodynamical analogues; there would thus be grounds for forming a theory of magnetism on the basis of mechanical phenomena, and a very important link in the chain of the correlation of the physical forces would be supplied.

While the experiments of Professor Bjerknes upon pulsating and rectilinearly vibrating bodies and their influence upon one another illustrate by very close analogies the phenomena of magnetism, those upon circularly vibrating bodies and their mutual influences bear a remarkable analogy to electrical phenomena; and it is a significant fact that exactly as in the case of magnetic illustration, the analogies are direct as regards the phenomena of induction, and inverse in their illustration of direct electrical action.

If we examine the figure produced by the field of force surrounding a conductor through which a current of electricity is being transmitted (see Fig. 1), we see that iron filings within that field arrange themselves in more or less concentric circles around the conductor conveying the current. From this fact Professor Bjerknes and his son, reasoning that, to produce a similar field of energy around a vibrating body, the vibrations of that body must partake of a circular or rotary character, constructed apparatus for producing the hydrodynamic analogue of electric currents, in which a conductor transmitting a current of electricity is represented by a cylinder to which oscillations in circles around its axis are given by suitable mechanical means, so as to cause the enveloping medium to follow its motion and make similar rotative vibrations. In some of the earlier experiments in this direction, cylinders carrying radial veins (A, Fig. 2) or fluted longitudinally around their surfaces (B, Fig. 2) were employed with the object of giving the vibrating cylinder a greater hold of the liquid in which they were immersed; but it was found that these vanes or flutings had but little or no effect upon water or liquids of similar viscosity, and Professor Bjerkes was led to adopt highly viscous fluids, such as Glycerin or maize sirup, both of which substances are well adapted for the experiments, being at the same time both highly viscous and perfectly transparent and colorless. In seeking, for the purpose of this research, a fluid medium which shall possess analogous properties to the luminiferous ether, or whatever may be the medium whose vibrations render manifest certain physical phenomena, it might be considered at first sight that substances so dense as glycerin and sirup could have but little in common with the ether, and that an analogy between experiments made within it and phenomena associated with ethereal vibrations would be of a very feeble description: but Professor Bjerknes has shown that the chief requisite in such a medium is that its viscosity should be great, not absolutely, but large only in proportion to its density, and if the density be small, the necessary viscosity may be small also. Neither is it necessary for the fluid medium to possess great internal friction, but what is necessary to the experiments is that the medium shall be one which is readily set into vibration by the action of the circularly vibrating cylinder; this property appears to be possessed exclusively by the more viscous fluids, and is, moreover, in complete accord with what is known of the luminiferous ether according to the theory of light.

The property is rather a kind of elasticity, which ordinary fluids do not possess, but which facilitates the propagation of transverse vibrations.

One form of apparatus for the propagation of rotative oscillations is shown to the left of Fig. 3, and consists of a cylinder, A, mounted on a tubular spindle, and which is set into circular oscillations around its axis by the little vibrating membrane, C, which is attached to the axis of the cylinder by a little crank and connecting rod shown in detail in Fig. 4. This membrane is set into vibration by a rapidly pulsating column of air contained in a flexible tube M, by which apparatus is connected to the pulsation pump which was employed by Professor Bjerknes in his earlier experiments. In Fig. 5, a somewhat similar apparatus for producing horizontal vibrations is shown, and marked N H C, the only difference between them being one of mechanical detail necessitated by the change in the position of axis of vibration from the vertical to the horizontal.

If circularly vibrating cylinders, such as we have described, be immersed in a viscous fluid and set into action, the following phenomena may be observed: 1. The effect upon the fluid itself, setting up therein a field of vibration, and corresponding by analogy with the production of a field of force around a wire conveying an electric current. 2. The effect upon other circularly vibrating bodies within that field of force corresponding to the action and reaction of electric currents upon one another. 3. The effect on pulsating and oscillating bodies similarly immersed, illustrating the mutual effects upon one another of magnets and electric currents. The first of these effects is one of induction, and, from what has been said from an earlier part of this article, it will be understood that the analogy between the hydrodynamic and the electric phenomena is direct and complete. The effects classified under the second and third heads, being phenomena of direct action (in the restricted use of the word), are uniformly analogous to the magnetic and electric phenomena which they illustrate.

(_To be continued._)

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THE XYLOPHONE.

Like most musical instruments, the xylophone, had its origin in very remote times. The Hebrews and Greeks had instruments from which the one of to-day was derived, although the latter has naturally undergone many transformations. Along about 1742 we find it widely in use in Sicily under the name of _Xylonganum_. The Russians, Cossacks, and Tartars, and especially the mountain population of the Carpathians and Ural, played much upon an instrument of the same nature that they called _Diereva_ and _Saloma_.

It appears that the xylophone was played in Germany as early as the beginning of the 16th century. After this epoch it was in use for quite a long period, but gradually fell into oblivion until the beginning of the present century. It was toward 1830 that the celebrated Russian Gussikow undertook a grand artistic voyage through Europe, and gained a certain renown and received many honors due to his truly original productions. Gussikow possessed a remarkable _technique_ that permitted the musical instrument which he brought into fashion to be appreciated for all its worth.

As the name, "instrument of wood and straw," indicates, the xylophone (which Fig. 1 shows the mode of using) consists of small pieces of wood of varying length, and narrow or wide according to the tone that it is desired to get from them. These pieces of wood are connected with each other by cords so as to form a triangular figure (Fig. 2) that may be managed without fear of displacing the parts. The whole is laid upon bands of straw designed to bring out the sounds and render them stronger and purer. The sounds are produced by striking the pieces of wood with a couple of small hammers. They are short and jerky, and, as they cannot be prolonged, nothing but pieces possessing a quick rhythm can be executed upon the instrument. Dances, marches, variations, etc., are played upon it by preference, and with the best effect.

The popularity of this instrument is making rapid progress, and it is beginning to be played in orchestras in France [as it has been in America for many years]. A method of using it has just been published, as well as pieces of music adapted to it, with piano, violin, orchestra, etc., accompaniment.

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ELECTROTYPING.

This eminently useful application of the art of electrotyping originated with Volta, Cruickshank, and Wollaston about 1800 or 1801. In 1838, Spencer, of London, made casts of coins, and cast in intaglio from the matrices thus formed; in the same year Jacobi, of Dorpat, in Russia, made casts by electro deposit, which caused him to be put in charge of the work of gilding the dome of St. Isaac at St. Petersburg.

Electrotyping for the purposes of printing originated with Mr. Joseph A. Adams, a wood-engraver of New York, who made casts (1839-41) from wood-cuts, some engravings being printed from electrotype plates in the latter year. Many improvements in detail have been added since, in the processes as well as the appliances. Robert Murray introduced graphite as a coating for the form moulds. He first communicated his discovery to the Royal Institution of London, and afterward received a silver medal from the Society of Arts.

BLACKLEADING THE FORM.

The process of electrotyping is as follows: The form is locked up very tightly, and is then coated with a surface of graphite, commonly known as blacklead, but it is a misnomer. This is put on with a brush, and may be done very evenly and speedily by a machine in which the brush is reciprocated over the type by hand-wheel, crank, and pitman. A soft brush and very finely powdered graphite are used; the superfluous powder being removed, and the face of the type cleaned by the palm of the hand.

TAKING THE MOULD.

A shallow pan, known as a moulding pan, is then filled with melted yellow wax, making a smooth, even surface, which is blackleaded. The pan is then secured to the head of the press, and the form placed on the bed, which is then raised, delivering an impression of the type upon the wax.

The pan is removed from the head of the press, placed on a table, and then built up, as it is termed. This consists in running wax upon the portions where large spaces occur between type, in order that corresponding portions in the electrotype may not be touched by the inking roller, or touched by the sagging down of the paper in printing.

MAKING THE DEPOSIT.

The wax mould being built, is ready for blackleading, to give it a conducting surface upon which the metal may be deposited in the bath, superfluous blacklead being removed with a bellows. Blacklead, being nearly pure carbon, is a poor conductor, and a part of the metal of the pan is scraped clean, to form a place for the commencement of the deposit. The back of the moulding is waxed, to prevent deposit of copper thereon, and the face of the matrix is wetted to drive away all films or bubbles of air which may otherwise be attached to the blackleaded surface of the type.

The mould is then placed in the bath, containing a solution of sulphate of copper, and is made a part of an electric circuit, in which is also included the zinc element in the sulphuric-acid solution in the other bath. A film of copper is deposited on the blacklead surface of the mould; and when this shell is sufficiently thick, it is taken from the bath, the wax removed, the shell trimmed, the back tinned, straightened, backed with an alloy of type-metal, then shaved to a thickness, and mounted on a block to make it type-high.

A RECENT IMPROVEMENT.

has been introduced in which there is added finely pulverized tin to the graphite for facing the wax mould; the effect in the sulphate of copper bath is to cause a rapid deposition of copper by the substitution of copper for the tin, the latter being seized by the oxygen, while the copper is deposited upon the graphite. The film is after increased by the usual means. Knight's expeditious process consists in dusting fine iron filings on the wet graphite surface of the wax mould, and then pouring upon it a solution of sulphate of copper. Stirring with a brush expedites the contact, and a decomposition takes place; the acid leaves the copper and forms with the iron sulphate a solution which floats off, while the copper is freed and deposited in a pure metallic form upon the graphite. The black surface takes on a muddy tinge with marvelous rapidity. The electric-connection gripper is designed to hold and sustain the moulding pan and make an electric connection with the prepared conducting pan of the mould only, while the metallic pan itself is out of the current of electricity, and receives no deposit.

BACKING-UP.

The thin copper-plate, when removed from the wax mould, is just as minutely correct in the lines and points as was the wax mould, and the original page of type. But it is obvious that the copper sheet is no use to get a print from. You must have something as solid as the type itself before it can be reproduced on paper. So a basis of metal is affixed to the copper film, and this again is backed up with wood thick enough to make the whole type-high. To get this, a man melts some tinfoil in a shallow iron tray, which he places on the surface of molten lead, kept to that heat in square tanks over ordinary fires. The tinfoil sticks to the back of the copper, and on the back of this is poured melted type-metal, until a solid plate has been formed, the surface of which is the copper facsimile and the body white metal. The electro metal plate, copper colored and bright on its surface, has now to go to the

FINISHING ROOM.

Here are two departments. In one the plates are shaved and trimmed down to fit the wood blocks, which are made in the other department. Some of these operations are done by hand, but it is very interesting to see self-working machines planing the sheets of metal to precisely the required thinness with mathematical exactness. A pointed tool is set to a certain pitch, and the plate of metal is made to revolve in such a way that one continuous curl shaving falls until the whole surface (back) has been planed perfectly true. The wood blocks are treated in the same way, after being sawn into the required sizes by a number of circular saws. Another set of workmen fit and join the metal to the wood, trim the edges, and turn the blocks out type-high and ready for working on the printing press.

A WET BLACKLEADING PROCESS.

In Messrs. Harper's establishment in New York, an improved wet process of blackleading is adopted. The wax mould is laid face upward on the floor of an inclosed box, and a torrent of finely pulverized graphite suspended in water is poured upon it by means of a rotary pump, a hose, and a distributing nozzle which dashes the liquid equally over the whole surface of the mould. Superfluous graphite is then removed by copious washing, an extremely fine film of graphite adhering to the wax. This answers a triple purpose; it coats the mould with graphite, wets it ready for the bath, and expels air bubbles from the letters. This process prevents entirely the circulation of blacklead in the air, which has heretofore been so objectionable in the process of electrotyping.

A NEW FOREIGN PROCESS.

The galvanoplastic process of M. Coblence for obtaining electrotypes of wood-engravings is as follows: A frame is laid upon a marble block, and then covered with a solution of wax, colophane, and turpentine. This mixture on the frame, after cooling, becomes hard, and presents a smooth, even surface. An engraved wooden block is then placed upon the surface of the frame, and subjected to a strong pressure. The imprint on matrix in cameo, having been coated with graphite, is then placed vertically in a galvanoplastic bath, and a cast, an exact reproduction of the wood-engraving, is obtained. The shell is then backed with type metal and finished in the usual way.--_Printer and Stationer._

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A NEW SEISMOGRAPH.

All the seismographs that have hitherto been employed have two grave disadvantages: they are either too simple, so that their indications are valueless, or too complicated, so that their high cost and delicacy, and the difficulty of mounting them and keeping them in order, tend to prevent them from being generally used.

Seismology will not be able to make any serious progress until it has at its disposal very certain and very numerous data as to telluric movements registered at a large number of points at once by accurate instruments. I have endeavored to construct a simple apparatus capable of automatically registering such facts as it is most necessary to know in scientific researches on the movements of the earth. After numerous experiments I believe that I have succeeded in solving this delicate problem, since my apparatus, put to the test of experience, has given me satisfactory results. I have consequently decided to submit it to the approval of men of science.

My seismograph is capable of registering (1) vertical shocks, (2) horizontal ones, (3) the order in which all the shocks manifest themselves, (4) their direction, and (5) the hour of the first movement.

The apparatus is represented in the accompanying cut. The horizontal shocks are indicated by the front portion of the system, and the vertical ones by the back portion. The hour of the first shock is indicated as follows: The elastic strip of steel, C, is fixed by one of its extremities to a stationary support, d. When, as a consequence of a vertical motion, the free extremity of this strip oscillates, the leaden ball, x, drops into the tube, c, and, on reaching the bottom of this, acts by its shock upon a cord, i, which actuates the pendulum of a clock that has previously been stopped at 12. The other strip, B, is very similar to the one just described, but, instead of carrying a ball, it holds a small metallic cylinder, u, so balanced that a vertical shock in an upward direction causes it to drop forward into the anterior half of the tube to the left. A second vertical shock in a downward direction causes it to drop into the other half. The cylinder, u, and the ball, x, are regulated in their positions by means of screws affixed to a stationary support.

The portion of the apparatus designed to register horizontal (undulatory) motions consists of four vertical pendulums, z z z z, each of which is capable of moving in but one direction, since, in the other, it rests against a fixed column.