Chapter 6

We show herewith the method employed by the Baltimore Car Wheel Company in casting chilled wheels to prevent tread defects. The ordinary mode of pouring from the ladle into the hub part of the mould, and then letting the metal overpour down the brackets to the chill, produces cold shot, seams, etc. In the arrangement here shown the hub core, A, has a concave top, B, and the core seat, C, is convex, its center part being lower than the perimeter of the top of the core. Figs. 3, 4, show the core, A, in the side elevation and in plain. Fig. 2 is a core point forming a space to connect the receiving chamber, E, above, with the mould by passageways, D D, formed in the side of the top of the core. The combined area of these passageways being less than that of the conduit, F, from the receiving chamber, the metal is skimmed of impurities, and the latter are retained in the receiving chamber, E. The entering metal flows first to the lower hub part at H H, thence by the sprue-ways, G G, to the lower rim part at J J, being again skimmed at the mouth of the sprue-ways. Thus the rim fills as rapidly as the hub, and the metal is of a uniform and high temperature when it reaches the chill.

In the wheels made by this firm, every alternate rib is connected with the rim, and runs off to nothing near the hub; the intermediate ribs are attached to the hub, and diminish in width toward the rim.--_Jour. Railway App._

* * * * *

ELECTRICITY AND PRESTIDIGITATION.

The wonderful ease with which electricity adapts itself to the production of mechanical, calorific, and luminious effects at a distance, long ago gave rise to the idea of applying it to certain curious and amusing effects that simple minds willingly style _supernatural_, because of their powerlessness to find a satisfactory explanation of them.

Who has not seen, of old, Robert Houdin's heavy chest and Robert Houdin's magic drum? These two curious experiments are, as well known, founded upon the properties of electro-magnets.

At present we shall make known two other arrangements, which are based upon the same action, and which, presenting old experiments under a new form, rejuvenate them by giving them another interest.

The first apparatus (Fig. 1), which presents the appearance of an ordinary round center table, permits of reproducing at will the "spirit rappings" and sepulchral voice experiments. The table support contains a Leclanche pile, of compact form, carefully hidden in the part that connects the three legs. The top of the table is in two parts, the lower of which is hollow, and the upper forms a cover three or four millimeters in thickness. In the center of the hollow part is placed a vertical electro-magnet, one of the wires of which communicates with one of the poles of the pile, and the other with a flat metallic circle glued to the cover of the table. Beneath this circle, and at a slight distance from it, there is a toothed circle, F, connected with the other pole of the pile. When the table is pressed lightly upon, the cover bends and the flat circle touches the toothed one, closes the circuit of the pile upon the electro-magnet, which latter attracts its armature and produces a sharp blow. On raising the hand, the cover takes its initial position, breaks the circuit anew, and produces another sharp blow. Upon running the hand lightly over the table, the cover is caused to bend successively over a certain portion of its circumference, contacts and breakages of the circuit are produced upon a certain number of the teeth, and the sharp blow is replaced by a quick succession of sounds, or a tremulous one, according to the skill of the medium whose business it is to interrogate the spirits. As the table contains within it all the mechanism that actuates it, it may be moved about without allowing the artifice to be suspected.

The table may also be operated at a distance by employing conductors passing through the legs and under the carpet and communicating with a pile whose circuit is closed at an opportune moment by a confederate located in a neighboring apartment.

Finally, on substituting a small telephone receiver for the electro-magnet, and a microtelephone system for the ordinary pile, we shall convert the rapping spirits into talking ones. With a little exercise it will be easy for the confederate to transmit the conversation of the "spirits" in employing sepulchral tones to complete the illusion.

Fig. 2 represents a device especially designed as a parlor ornament. When the plant is touched, the insects resting upon it immediately begin to flap their wings as if they desired to fly away. These insects are actuated by a Leclanche pile hidden in the pot that contains the plant. The insect itself is nothing else than a mechanism analogous to that of an ordinary vibrating bell. The body forms the core of a straight electro-magnet, _c_, which is bent at right angles at its upper part, and in front of which is placed a small iron disk, _b_, forming the animal's head. This head is fixed upon a spring, like the armature of ordinary bells, and causes the wings to move to and fro when it is successively attracted and freed by the electro-magnet. The current is interrupted by means of a small vibrating device whose mode of operation may be easily understood by glancing at the section in Fig. 2. The current enters the electro-magnet through a fine copper wire hidden in the leaves and connected with the positive pole of the pile. The negative pole is connected with the bottom of the pot. The wire from the vibrator of each insect reaches the bottom of the flower-pot, but does not touch it. A drop of mercury occupies the bottom of the pot, where it is free to move about. It results that if the pot be taken into the hand, the exceedingly mobile mercury will roll over the bottom and close the circuit successively on the different insects, and keep them in motion until the pot has been put down and the drop of mercury has become immovable.

* * * * *

PORTABLE ELECTRIC SAFETY LAMPS.

One of the most difficult problems that daily presents itself in large cities is how to proceed without danger in the search for leakages in gas mains, or in attempts to save life in houses accidentally filled with explosive gases. The introduction of a flame into such places leads in the majority of cases to accidents whose consequences cannot be estimated. The reader will remember especially the explosion which occurred some time ago in St. Denis Street, Paris, and which killed a considerable number of persons. It has, therefore, been but natural to think of the use of electricity, which gives a bright line without a flame, in order to allow life-saving corps and firemen to enter buildings filled with an explosive mixture, without any risk whatever.

Several electricians have proposed ingenious portable apparatus for this purpose, and, among these, Mr. A. Gerard, whose device we illustrate herewith. In this system the electric generator is stationary, and remains outside the building. This, along with all the rest of the apparatus, is mounted upon a carriage. The operator, instead of carrying a pile to feed the lamp, drags after him a very elastic cable containing the two conductors. This "Ariadne's thread" easily follows all sinuosities, and adapts itself to all circumvolutions. The entire apparatus, being mounted upon a carriage, can be easily drawn to the place of accident like a fire engine.

_General Description_.--Fig. 1 shows the carriage. In the center, over the axle, is mounted a dynamo-electric, machine, D, driven by a series of gear wheels that are revolved by winches, MM. Upon the shaft, A, is fixed a hand wheel, V, designed to regulate the motion. In the forepart of the carriage are placed two windlasses, TT, permanently connected with the terminals of the dynamo. Upon each of these is wound a cable formed of two conductors, insulated with caoutchouc and confined in the same sheath. Each windlass is provided with five hundred feet of this cable, the extremity of which is attached to two lanterns each containing an incandescent lamp. These lanterns, are inclosed in boxes, BB, with double sides, and cross braced with springs so as to diminish shocks. Under the windlass there is a case which is divided into two compartments, one of which contains tools and fittings, and the other, six carefully packed incandescent lamps, to be used in case of accident to the lanterns. At the rear end of the carriage there is a hinged bar, C, designed to support it at this point and give it greater stability during the maneuvers. The stability is further increased by chocking the wheels.

_Maneuver of the Apparatus_.--The carriage, having reached the place of accident, is put in place, its rear end is supported by the bar, C, the wheels are chocked, and the winches are placed upon the dynamo gearing. Two strong men selected for the purpose now seize the winches and begin to revolve them, and the lamps immediately light while in their boxes. Another man, having opened the latter, takes out one of the lanterns and enters the dangerous place, dragging after him the elastic cable that unwinds from the windlass. Two men are sufficient to turn the winches for five minutes; with a force of six men to relieve one another the apparatus may therefore be run continuously.

The dynamo, which is of strong and simple construction, is inclosed in a cast iron drum, and is consequently protected against accident. With a power of 25 kilogrammeters it furnishes a current of 40 volts and 7 amperes, which is more than sufficient to run two 50-candle incandescent lamps. The winches are removable, and are not put upon the shaft until the moment they are to be used.

The windlasses, as above stated, are permanently connected with the terminals of the dynamos. The current is led to them through their bearings and journals. Their shaft is in two pieces, insulated from one another. One extremity of the cable is attached to these two pieces, and the other to the lantern. Each windlass is provided with a small winch that allows the cable to be wound up quickly.

The two lanterns are different, on account of the unlike uses to which they are to be put. One of them is a hand-lamp that permits of making a quick preliminary exploration. The second is to be fixed by a socket beneath it to a pole that is placed along the shafts of the carriage. This lantern, upon being thrust into a chimney, shaft, or well, permits of a careful examination being made thereof. As the handle terminates in a point; it may be stuck into the ground, to give a light at a sufficient height to illuminate the surroundings.

The hand lantern consists of a base, P, provided with three feet. At the top there is a threaded circle to which is attached a movable handle, K, that is screwed on to a ring, C. These three pieces, which are of bronze, are connected by 12 steel braces, E, that form a protection for the glass, M. The lantern is closed above by a thick glass disk, G. The luminous rays are therefore capable of spreading in all directions. Tight joints are formed at every point by rubber or leather washers.

In the center of the lantern is placed the incandescent lamp. This is held in a socket, and is provided with two armatures to which the platinum wires are soldered. Two terminals, b, are affixed to the lamp socket. Beneath the lantern there is a cylindrical box provided with a screw cap. In one side of this box there is a tubulure that gives passage to the electric cable whose conductors are fastened to the terminals. A conical rubber sleeve, R, incloses the cable, which is pressed by the screw cap, S. A special spring, Y, attached at one end to the top of the lantern, and at the other to the cable, X, is designed to deaden the too sudden shocks that the lantern might be submitted to, and that would tend to pull out the cable.

As a result of the peculiar arrangement of this lantern, the lamp is constantly surrounded with a certain quantity of air that would certainly suffice to consume the carbons in case of a breakage of the globe without allowing any lighted particles to escape to the exterior. Besides, should the terminals become unscrewed, and should the conductors thus rendered free produce sparks, the latter would be prevented from reaching the exterior by reason of the absolute tightness of the box. In case the incandescent lamp should get broken, the only inconvenience that would attend the accident would be that the man who held the lantern would be for a moment in the dark. When he reached the carriage, it would be only necessary for him to take off the glass disk, take the broken lamp out of its socket, insert a new one, and then put the glass top on again.--_Le Génie Civil_.

* * * * *

Voltaic batteries containing solutions of ammonium chloride and zinc chloride can, according to the recent researches of M. Onimus, be converted into dry piles by mixing these solutions with plaster of Paris, and allowing the mixture to solidify. If mixtures of ferric oxide and manganese peroxide with plaster of Paris are employed, the electromotive force is slightly higher than with plaster of Paris alone; and when ferric oxide is used, the battery quickly regains its original strength on breaking the circuit. When the battery is exhausted, the solid plaster of Paris has simply to be moistened again with the solution.

* * * * *

THE ELECTRIC DISCHARGE AND SPARK PHOTOGRAPHED DIRECTLY WITHOUT AN OBJECTIVE.

The study of the form and color that electric discharges exhibit, according to the different ways in which they are produced, has already enticed a certain number of amateurs and scientists. Every one knows the remarkable researches of the lamented Th. Du Moncel on the induction spark, and during the course of which he, in 1853, discovered that phenomenon of the electric efflux which has since been the object of important researches on the part of several physicists and chemists, among whom must be cited Messrs. Thenard, Hautefeuille, and Chapuis. Twenty years ago, Mr. Bertin, who was then Professor at the Faculty of Strassburg, and who was afterward subdirector of the normal school, was directing his researches upon the electric discharges produced by high tension apparatus, plate machines, and Leyden jars. He thought, with reason, that, on account of its rapidity and complexity, a portion of the phenomenon must escape the eye of the observer, and so the idea occurred to him to photograph the discharge in order to afterward study its forms more at his leisure. We have recently had an opportunity of seeing a negative which was obtained by him at that epoch; but the photographic processes then in use probably did not allow him to obtain others that were as satisfactory, and he had given up this kind of study, when, last year, he had an opportunity of speaking of it to the well known manufacturer Mr. F. Ducretet, whom he induced to take it up and employ the new gelatino-bromide process. Unfortunately, he died before these experiments were begun, and was unable to see the realization of his project. Mr. Ducretet did not abandon the idea, but constructed the necessary apparatus, and obtained the results that we now place before our readers.

His apparatus, which contains no photographic objective, consists of an oblong case, ABCD, made of red glass and resting upon an ebonite table supported by one leg (Fig. 1). In the top of the case, as well as in the two sides, AD and BC, are apertures that are closed by ebonite cylinders through which slide, with slight friction, copper rods, HLN. In the leg of the table there is a copper rack which may be maneuvered from the interior by a pinion, and which communicates electrically with a terminal, E. The upper part of this rack, which enters the glass case, is threaded, so that there may be affixed to it either a metallic or an insulating disk. The rods, HLN, are likewise threaded, so that there may be affixed to their internal extremities balls, points, combs, and disks of metal or of insulating material at will.

In short, we have here a transparent box (impermeable to photogenic rays) into which electricity may be led by means of four conductors that are arranged two by two in a line with each other, or in perpendicular positions, and that may be made to approach or recede from one another by maneuvering them from the exterior. This very simple arrangement answers every requirement, and, upon placing a sensitized plate in the vicinity of the conductors, permits of photographing the electric discharge directly and, so to speak, before the eyes of the operator.

As a source of electricity, use is made of a bichromate of potash battery of 6 elements, capable of giving 10 volts and 15 amperes. The current from this battery is converted into a current of high tension by means of a strong induction coil capable of giving sparks more than eight inches in length. The discharge shown in Fig. 4 was obtained by means of a Holtz machine. Each experiment lasted less than a second.

Figs. 2 and 3 represent the efflux that occurred under; the following conditions: The disk, P, was of metal, and was connected with the negative pole of the induction coil; and upon it was laid the photographic plate with the sensitized film downward, and consequently touching the disk. This is what produced the opaque circle in the center. Then the photographic plate was entirely covered with a thin ebonite plate, above which there was a second one supported by small wedges, so as to allow air to circulate between them. Finally, upon this second ebonite plate there was placed another photographic plate, with its sensitized film upward and directly in contact with an upper metallic disk, and connected with the positive pole of the coil by the conductor, L. An inspection of Figs. 2 and 3 shows that the, efflux does not possess the same form at the two poles. We remark at the positive pole a quite wide opaque circle surrounded by a sort of aureola composed of an infinite number of very delicate rays, while at the negative pole the aureola seems not to have been able to spread. We see, moreover, the same phenomenon in examining Fig. 4 (which represents the efflux obtained by means of a Holtz machine), but this time in a horizontal direction. The photographic plate was here placed upon the non-conducting disk, P. As the sensitized film was upward, it was put in contact with the balls at the extremity of the conductors, H and N.

It will be seen here again that the efflux spreads out widely at the positive pole, while it is contracted at the other. The conducting balls were spaced 0.04 inch apart. A spark leaped from one to the other at the moment the current was being interrupted.

In Fig. 5 we are enabled to study with more ease a spark obtained with nearly the same arrangement. The balls, H and N, did not here rest directly upon the sensitized film, but upon two small sheets of tin cemented to the extremities of the plate at 0.06 inch apart. In addition, the source employed was not the Holtz machine, but the pile with induction coil. Two nearly parallel sparks were obtained. It will be seen that these are very complex. Each of them seems to be formed of four lines of different sizes, entangled with one another and presenting different sinuosities. Aside from this, the plate is traversed for a space of 0.04 of an inch by curved lines running from one pole to the other, and exhibiting numerous sinuosities.

Fig. 6 represents a discharge that occurred under the following circumstances: The disk, P, being metallic and connected with one of the poles, there was placed upon it a thin ebonite plate of the same dimensions as the photographic one, and then the latter with the sensitized pellicle upward. Finally, the pellicle was put in contact with the upper conductor, L, which terminated in a ball and was connected with the other pole of the induction coil.

It will be seen that, despite the two dielectrics (ebonite and glass) interposed, and the opacity of one of them, the efflux that occurred around the disk, P, is quite sharply reproduced upon the sensitized plate by a circle like that which we observed in Figs. 2 and 3. It will be seen, besides, that an infinite number of ramifications in every direction has been produced around the ball, and we can follow the travel of the spark that leaped between the ball and disk in two directions situated in the prolongation of one another.

Under the two principal and clearly marked lines that this spark made there are seen two other, very pale and much wider ones, that present no sinuosities parallel with the first.

The results of these experiments are very curious. The position of the plates was varied in 18 different ways, as was also the form of the conductors. We have spoken of those only that appear to us to present the most interest. Unfortunately, notwithstanding the skill of the engraver, it is impossible to render with accuracy all the details that are seen upon examining the negative. The proofs that have been printed upon paper present much less sharpness than the negative, for there are certain parts of the figures on the glass that do not show in the print.

We have been content here to make known the results obtained, without drawing any conclusions from them. It is to be hoped that these experiments, which can be easily repeated by means of the apparatus described above, will be repeated and discussed by electricians, and that they will contribute toward making known to us the nature of the mysterious agent that will give its name to our era.--_G. Mareschal, in La Lumiere Electrique._

* * * * *

THE TRUE CONSTANT OF GRAVITY.

Many of the readers of this journal may like to participate in the discussion of the following proposition. The statement is this:

The space through which a body, near the surface of the earth, at mean latitude, _in vacuo_, descends by virtue of the accelerating force of gravity in 1/1000 of an hour is precisely 2,500 geometric inches = 100 geometric cubits = the side of a square geometric acre.

[The geometric inch is taken, in accordance with the view of Sir John Herschel, at 1/1,000,000,000 of twice the polar axis of the earth, and equals 1-1/1000 English inches very nearly.]

The strict decimal relation of the proposition is shown by the following table. It has been tested by Clairaut's theorem, and by other existing expressions, and has been found to agree, far within the probable limits of errors in observation, with the most approved values of the constant. In fact, it is contained in the existing expressions; but the _decimal_ relation does not appear unless we state the unit of linear measure as a decimal of the earth's semi-polar axis, and, at the same time, divide the circle, both for time and for general purposes, _geometrically, i.e._, by strict decimalization upon the hour-angle. A mathematical reason underlies the proposition.