There are many toys which one meets with in the scientific stores, the making of which for themselves would give great satisfaction to enterprising devotees of the electrical art. They are for the most part easily constructed, and a great deal of amusement can be derived from them. I have my doubts whether the fathers and mothers of the amateur electrician will thank me for introducing the subject of the present article, but they must take comfort in the thought that if it works well it shows real constructive power on the part of the maker.
For the benefit of those whose capability of working in metal is limited, I am first going to describe the making of this remarkable instrument in its simplest form—a form, in fact, so simple that any one can make it and achieve success in a few hours.
First of all we want an old tooth-powder box. These are all made the same size, and consequently it is unnecessary to give dimensions. The top of the tooth-powder box is to be taken, and by means of a fretsaw (this invaluable tool should be in the hands of every boy who likes carpentering; there are many uses to which it can be put quite different for what it is intended for) a circular hole is to be cut out about ? inch less than the inside—that is to say, a rim of about ? inch is to project all around from the rim of the lid.
We now want what is known in photography as a “ferrotype” plate—i. e., a piece of very thin sheet iron. Most dealers in photographic goods will not sell less than four or five dozen of them, and this is too many for us. A photographic friend will let us have one gratis, or a professional photographer may agree to part with one for five or ten cents if he is attacked when in a good temper.
The ferrotype plate having been procured by some means or other, the next thing is to cut from it a circle just small enough to go inside the rim of the top of the tooth-powder box. You can mark out the circle before cutting it by painting the top of the rim of the bottom of the tooth-powder box with ink and pressing it down on the ferrotype plate, when enough ink will come off to guide the scissors, and of course the circle so cut will be the exact size required.
We now have to make the motive power of the machine, for there is plenty of work done in it, though it only makes a noise—no one can “make a noise in the world” without doing plenty of work! And to make this we take a piece of soft iron rod about 1½ inch long and half an inch in diameter, and cut two circles out of cardboard 1¾ inch in diameter. The soft iron rod can be bought from any hardware store, and it ought to be quite soft enough to work at once without doing anything to it; if it is not, it must be heated red-hot in a good fire and left among the coals over-night to get cool very gradually.
Personally I have always found that the ordinary bars of soft iron bought from any hardware man are amply soft enough for any electrical work.
You must get the hardware man to file the ends of your bar flat; if they are not filed you will have to do it yourself, and a fine job it is!
Now we go back to the circles of cardboard. A hole is to be cut in each in the center exactly the size to admit the core of soft iron, then by slipping the circles over the ends we get a reel. Now a hole has to be made exactly in the center of the bottom of the tooth-powder box, and exactly so large that the core of soft iron will fit tightly into it; you can do this again with the fretsaw, the wood of which tooth-powder boxes are made is delightfully easy to cut.
Now comes the adjustment of the reel. You must put the circles on the core, and putting one end of the latter through the hole at the bottom of the box you must push the iron through until the top is exactly flush with the top of the rim of the side of the box. One of your circles will now be much further on the core than the other, and the one at the end that is not pushed through the hole must be adjusted close to the edge, leaving about 1/16 of the core projecting, so that we have now a reel formed at one end of the core, and held in position by the bottom of the box. The more stiffly the core fits the hole the better, and if it has to be hammered into its place, better still, only take care not to split the wood of the bottom of the box.
The circles, being now in their right places, must not be moved again, but the roller has to be wound with wire, for which purpose the core will have to come out of the box temporarily. Before beginning to wind the wire, get some thin paper (French note-paper is best), and wind a piece round and round the core between the circles, fastening it and the circles at its ends to the core by means of a small quantity of mucilage.
We now have to wind the wire on to the roller. The more wire the stronger the magnet will be, but sufficient will be about two ounces. You can get the wire at most hardware stores for fifteen cents an ounce. It is generally cotton-covered, of light green color; medium thickness should be used, not too fine, as this offers too much resistance to the current, and not too coarse, or it will fill the reel too soon.
We begin by making a hole near the core in the circle which is furthest on it, and push one end of the wire through a hole from the inside of the reel. About three inches should be pushed through to allow for future manipulation, and the wire is now to be wound tightly over the paper covering the core in even coils, layer on layer, till the reel is nearly full and we have arrived at within about three inches of the other end of the wire. This is now to be passed through another hole in the same circle as before, which hole will of course be further from the center than the first. The magnet will be much stronger if two or three folds of paper are wrapped round it between each layer of wire.
The coil is now constructed, and can be replaced in the tooth-powder box, passing the ends of the wire through two holes in the side or bottom made to receive them. Before leaving this part of the instrument I may remark that care must be taken that the covering of wire is quite continuous throughout, and has not got rubbed off at any points; if it has, you must wind fine silk over it to cover it up again. Should there be a break anywhere in the wire you must carefully scrape the wire off the two ends and twist the wires firmly together, if possible soldering them together and then wind fine silk over the join.
It is not necessary in this machine to soak the coil in melted paraffin, but might improve the insulation if the cover of the wire is thin. Only if there is a join and you have twisted, not soldered the wires together, you must not soak the coil in wax, or the melted wax gets between the ends of the wires and stops the current (this of course applies to all electro-magnets and should be remembered as a possible cause of failure.)
The core having been pushed through the hole again, up to the circle of cardboard, the ferrotype plate is placed in the top of the box, and the box is shut up. Now the ferrotype plate must be exactly free of the end of the core and that is all. You can test this by tapping it. If it vibrates in and out, it is all right; if the end of the core is too tightly pressed against it, there will be no possibility of moving the center in and out, and the core must be driven further through the hole till it is just free of the ferrotype plate.
Fig. 1.—Shape of Platinum Foil, p, Fastened to Ferrotype Plate, f.
Now comes another part of the instrument, viz., the contact-breaker. The following is as good a way of arranging it as any: Take a piece of sheet brass the exact length of the diameter of the top of the tooth-powder box and about half inch wide, and in the middle of it bore a hole which will admit a brass screw—with a milled head preferably. The screw should fit tightly into the hole, so as to screw easily up and down when turned. To the end of the screw, which is cut off flat, is soldered a short piece of platinum wire, inserted in a hole in the end of the screw made to receive it; it can be fastened by any other means, as long as it will screw up and down and is in contact with the brass screw. Adjust the screw so that the platinum point is within a minute distance of the ferrotype plate when the brass support is screwed down at the ends to the side of the box lid, and screw it down with small screws firmly in its position.
Fig 2.—Section of Simple Electric Trumpet Showing Details of Various Parts.
A, Tooth-powder box. B, Electro-magnet. C, Brass Screw. D, Flange for screw. E, Brass support for screw. F, Ferrotype plate. G, Wire attached to brass strip supporting screw. H, Wire from end of coil attached to platinum foil at P. I, Wire from the other end of coil passing through bottom of box.
Before this is done, however, a thin strip of platinum foil should be soldered to the upper surface of the ferrotype plate, or otherwise fastened to it—elastic glue will answer—this strip terminating in the center, and reaching to the edge of the plate, leaving a short piece over. A very thin strip will be enough, of the shape of P in Fig. 1. Now the ferrotype plate is to be placed in position again (the side of which the platinum foil is fastened being outwards, and the end of the foil going down between the edge of the ferrotype plate and the wood into the inside of the box), and the end of the wire from the coil which was left inside the box is to be securely fastened, either by soldering or otherwise, to the end of the platinum foil which was left loose, so as to be in metallic connection with it. A wire can now be twisted round or soldered to the screw with the platinum point, and the instrument is complete.
It has taken some space to describe, but I made my own in about half an hour. Fig. 2 gives a general view of the parts put together.
The lid of the box should be tightly fastened down by four small screws, two of which may be those which fasten on the brass strip holding the screw.
Now to consider its action. The wire I in Fig. 2 is connected to one wire of the battery, and the wire G to the other. The current then starts from the battery, round the coil B, converting the core into a magnet, and up the wire H to the platinum foil P, along the platinum foil, which was fastened to the upper side of the ferrotype plate F, to the platinum wire which tips the screw C. It then goes up the screw C, along the brass piece E, which is fastened to the box by screws, as shown in the figure, to the wire G, and so back to the battery by the other wire.
The screw C must be therefore screwed down till the platinum wire at its tip is just in contact with the foil on the ferrotype plate. Now of course when the current goes round the coil, and thus converts the soft iron into an electro-magnet, the latter instantly attracts the ferrotype plate which is immediately above it. But the latter moving its center near the core, the platinum foil which is attached to it is thereby moved out of contact with the wire on the screw C, and the current is instantly stopped. Thereupon the attraction of the magnet ceases, and the ferrotype plate flies back to its former position and so joins the platinum wire and foil, and starts the current again, and the former process is repeated. The ferrotype plate therefore vibrates with tremendous rapidity between the core and the platinum screw. Now the vibrating armature of an ordinary coil makes quite a hum when hard at work, but of course a large plate such as this makes a much louder noise, consequently you will hear a ferocious buzzing like an army of millions of bees let loose from a hive, and on screwing the screw C up or down till you get to the correct point you will get a shrill note very like a penny whistle. If screwed up the vibrations are slower, and a deeper note is produced; if screwed down the vibrations are more rapid and a higher note is sounded. Therefore you can amuse yourself by screwing it rapidly up and down, or adjusting it by pressing the brass piece with your finger, and a little practice will enable you to bring out a sort of tune produced by electricity!
When you have become tired of jingling out your tune you can fix the electric trumpet up in a permanent position, adjusting the wires from the battery so as to pass through an ordinary “press” which may be in another room. The trumpet will then begin buzzing or hooting whenever the button of the press is pushed in, and stop when the pressure is released. In this way of course the trumpet will act as a “call” instead of a bell, and as the double wire can be easily hidden under the carpet and in dark corners, and painted to match whatever wood-work it crosses, you can arrange it from an up-stairs room to a down-stairs one or vice versa with very little trouble. I give an illustration of the method of connecting the battery and trumpet with one switch or “press,” to show how to arrange the series. (See Fig. 3.)
Fig. 3.—Method of Connecting Trumpet to Battery and One Press.
When the button P is pushed in, the spring A touches the metal piece B, and completes the circuit. On removing the finger from P, the spring separates from B, and the current is stopped. P, Press. L, Battery. T, Trumpet.
The trumpet made in the very simple way I have described will not produce a very loud noise, but quite loud enough, if properly put together, to attract a person’s attention who was in the room when it went off. The sound can be rendered louder by fixing a cardboard funnel or “cornucopia” to the front of the tooth-powder box to make a kind of horn.
PART II.
The trumpets sold in the shops, as a rule, make a very loud noise indeed—in fact, a little of it goes a very long way with most people. The increased sound is probably due to the body of the trumpet being composed of brass, which, vibrating in unison with the ferrotype plate, increases the sound. Wood will therefore not give so loud a sound, and if you can construct the case of metal you should certainly do so. The vibrations of the plate, and therefore the sound, may also be increased by using a horseshoe magnet, the two poles attracting the plate more strongly. In the bought trumpets the case is shaped like a horn, in which the magnet is placed, the platinum contact-breaker being behind (where it is in the one I have described, supposing there was no bottom to the box and the magnet was supported by a bar across from side to side, the cornucopia being placed on that side of the box, instead of the other, with the magnet inside it). I think it is unnecessary to describe their construction further, as the principle and details of construction of the simple one I have described will apply to any, and any method of structure may be adopted which suits the mind of the maker.
The trumpet having been made I will now give you a plan of fitting it up which adds enormously to the effect. We want to hide the trumpet so that no one shall know where it is. My own plan of doing this is as follows: I have made a wooden erection, of which I give a drawing which will explain itself. It consists of a back with a shelf at the bottom and a kind of canopy at the top. It can be made almost any size, small or big, to suit the occupant of the shelf. My own measurements are about as follows: From the top A to the bottom B, the length of back piece, including bracket, 1 foot 3 inches. Breadth of back 5¼ inches. Side of canopy (D), breadth 4½ inches, height 3½ inches, breadth of front (C to D) 5¼ inches; height of course the same as sides. The top piece will then be about 5¼ inches by 4½ inches. The shelf at the bottom is about the same size as the top of the canopy, and is supported by a bracket of rather thick wood, which you can carve as elaborately as you like.
Now take the electric trumpet, whether made at home or purchased, and fasten it to the under side of the canopy (this is best done before the sides are put on), and fasten a double wire behind the back (cutting a groove for it to go in) up to the back of the canopy, where it goes through and divides, one wire being fastened to one terminal of the trumpet and the other wire to the other. The double wire goes right down the back and emerges at B. Obviously if you now join your press and battery on to the double wire, when you squeeze the press the trumpet will squeak. But here we are going to practice a little innocent deception, and to that end we go to a toy shop and purchase a small and pretty doll of the male sex, and if you can get one (or dress one up) attired as a soldier or trumpeter, by all means do so. The doll is now to be fixed on to the bracket by means of a long wire—say a hairpin bent out straight, one end being pushed into the wood, the other passing up one trouser leg of the doll and into its body; the wire is thus completely hidden and is much better than glue, as it admits of the doll being placed in a natural attitude, and being removed if required. In one of his hands you must make him hold a small trumpet (this is a very expensive item; it will cost two cents) with the mouthpiece to his mouth, as represented in the picture.
Fig. 4.—Electric Doll.
(Letters as referred to in text.)
The whole thing is now fastened to the wall in a convenient place, by driving nails through the back, and the double wire is completely hidden by passing it behind furniture, books, etc., down to the floor. There is great scope for ingenuity on the part of the worker in hiding the wire, and no definite instructions can possibly be given. In my own case I have no back piece below the shelf the support being against the wall. The wire descends behind the support (to B in the picture), and below that I have hung a “date calendar” over it, it makes a turn to the right and goes down behind a chiffonier covered with books to the floor. Under these circumstances no human being could possibly tell that there was a wire at all, and there being no back piece under the bracket (so that the paper of the room can be seen), nothing but the support touching the calendar, it does not look as if any wires could possibly be hidden anywhere.
Now, if you press the button, of course the trumpet squeaks, but the doll being just underneath it, and the trumpet being in the dark under the canopy, no one thinks it is a separate instrument, but of course every one jumps to the conclusion that it is the doll blowing! Hide the battery in a corner in a black box, the wires coming through the side next the wall, and the press in a dark corner, or on the floor under a table so that you can put your foot on it while your hands are free, writing, etc.
You can of course now tell the doll to blow, at the same moment putting your foot on the press, when the trumpet blows accordingly. Of course this is mysterious to the last degree to the uninitiated friend to whom you are displaying the doll, as you may be any distance off from the doll with your hands free, speaking to him across the room.
The wooden erection to hold the doll can be painted any color; preferable the back should be black, as it shows off the doll. In front of the canopy you can paint a monogram or heraldic device. If the doll is one of those extremely pretty little specimens which can be procured at any good toy shop for about twenty-five cents, dressed as base ball players, soldiers, etc, (what our grandmothers would have thought of them in their young days it is difficult to imagine) it will really be quite an ornament to the room, independently of its electrical qualities.
This chapter has outgrown the space I meant to occupy, and I must wait for the next to tell you how to make the doll work from various parts of the room as you walk about and talk to him, and how to make the battery. The best battery to use is to Leclanche. You can use three or four cells of No. 2 size according to length of wire through which the current has to pass.
In my next chapter I will try and explain how to make an electric drum, so that you can have a kind of drum and fife band.
PART III.
THE ELECTRIC DRUM.
In part two on the “Electric Trumpet,” I promised to explain how to make an electric drum; and this promise I now propose to redeem.
The system on which it works is precisely analogous to that of the electric trumpet, and almost identical with that of the ordinary electric bell, of which I hope to say more in another chapter.
As before, we have a hammer vibrating backwards and forwards in response to pulls from a magnet, which is magnetized and demagnetized by stopping and starting an electric current. In the case of the induction coil, the hammer is only a means whereby the current is broken and started again with great rapidity, and in the case of the trumpet the vibrator is used to make the noise by its vibration, but in this instrument we must have a bona fide hammer, which must be able to beat the drum, and thus cause a stirring and martial sound.
First, then, we will devote our attention to the construction of the magnet. In former chapters (as in the case of the electro-motor for example), I have given you the method of making the magnets out of one solid piece of soft iron, in the form of a horseshoe. This time, however, we will make it of several pieces, for a change; it is far more convenient to make, and looks much neater when finished.
Take a piece of soft iron 1½ inches long by ? inch broad and ? inch thick, and in the middle drill a hole about 3/16 inch in diameter. On each side of this, on a line with it at a distance of about ¼ inch, drill two more holes of the same size. This is to form the back, or, as it is scientifically termed, the yoke of the magnet. To form the poles we require two exactly similar pieces of soft iron bar 1½ inch long and ? inch in diameter. These are to be filed quite smooth at the ends after cutting, and in the middle of one end a hole is to be drilled to admit a screw which will just go through the holes on each side of the center one made in the flat piece of the soft iron. These holes are cut to receive the thread of the screw, but if you can’t do this you can simply leave out the end holes for screws, and solder the round and flat pieces of iron together. These are to be soldered or screwed together, so as to form a magnet, the hole in the middle of the flat piece serving to introduce a screw, for the purpose of attaching the magnet to a support. The best plan, if you can do it, is to drill and “tap” this hole to receive a screw which is inserted in a brass support made of a piece of brass 1? inch long, ½ inch broad, and ? inch thick, bent at right angles at about ½ inch from one end, this shortest end being drilled for two screws to fasten it to the base-board, while the longest end has a hole in the center about ? inch from the end, to admit the screw which fits the hole in the center of the yoke. Having done all this, you will have Fig. 1, which represents the magnet before it is wound.
Fig. 1.—Magnet Put Together Ready for Winding.
(Sectional diagram.)
A A, Circular bars of soft Iron. B B, Flat bars of soft iron forming the “yoke.” C, Brass support for magnet. S S S, Screws fastening parts of magnet together.
The soft iron cores have now to be converted into magnets as usual, and here comes in the especial advantages of having screws to fasten the magnet together, as you can take the whole thing to bits, wind the wire on the legs in comfort, and then fasten together again. But if you have soldered the magnet together, you can achieve the same end in a different way by making two small bobbins to hold the wire, the exact size to slip on over the soft iron cores when the wire is wound on them. It is generally considered proper to wind the wire on bobbins, which can be removed from the cores if required. I should think it can seldom be required, but the bobbins are convenient in this case. I may remark parenthetically that bobbins wound and unwound, soft iron cores, and yokes, separately or together, and supports fixed to the yokes or not, can be obtained from any large electrician who sells parts of electric bells, etc.; the magnet can also be got put together complete.
We now have to make bobbins, supposing that we are not going to buy them. The elaborateness of their manufacture will depend entirely on the skill of the maker. Some construct them by sawing off top and bottom of a reel of cotton, and forming a roller of cardboard to fit the magnets, finally joining the ends of the reel to this roller, to make an elongated reel of the right size. Others construct their bobbins entirely of cardboard, the ends being merely two circles of card. Others who are versed in the mysteries of wood-turning, and are lucky enough to possess a lathe with which to do it, make two bobbins of solid wood, drilled to fit the iron cores. For these no instructions are needed, as the dimensions will be as given presently. For those who only want to use the magnet for this special purpose, and do not care about the bobbins being removable, the following is the simplest way to set to work:
Fig. 2.—Magnet Wound and Put Together.
A A, Soft iron cores. B B B B, Ends of bobbins, on which wire is wound as shown. C C, Yoke of magnet fastened to support and held up by D, bottom of brass support, with holes for screws. E, Joined ends of wires. F F, Exterior ends of coils. The arrows show relative directions in which the two coils are wound.
Cut two circles of thick cardboard, each ? inch in diameter, and in the center cut a hole the exact size to slip over the soft iron core. Now wrap several thicknesses of thin tissue paper—or preferably French note paper or tracing paper—over the magnet, between the circles of cardboard, cutting the strip about 1? inch broad or ? inch less than the length of the cores. Now you can fasten the two circles of cardboard at the ends of the tracing paper, and keep them in their proper places on the magnet by means of mucilage—beat the soft iron before applying, and it will then adhere firmly to it. In this way, of course, you form a roller, on which we now have to wind the wire. If you have soldered the magnet’s parts together, you must have movable bobbins, as it would be simply impossible to wind the wire evenly on the cores when fixed in position, as the edges of the bobbins will be so close together that it is not possible to wind the wire on between them without the coils becoming displaced.
The method of winding the wire is simple enough. No. 24 wire is a good size to use; it can be cotton-covered or, preferably, silk-covered, as in the latter case the insulation is better. Begin by making a hole near the roller in the circle of cardboard that is next to the end where the hole for the screw has been made. Pass about three inches of wire through the hole and then wind it evenly on over the tracing paper from end to end and back again. You ought to have five or six layers of it; an ounce, or an ounce and a half, of wire will probably be enough. When it is all on, make another hole in the disc and pass out the wire. This is only to hold it safe while you wind the other bobbin. When that is finished you can put the magnet together, and ends of the two wires have now to be joined together. The two ends that are joined together must be those which come from the wire that is wound from the right to the left over one core and left to right over the other, that is to say, taking the wire when joined as one, it must be so wound on both limbs of the magnet that if they were bent into one straight bar it would all be wound in the same direction.
Fig. 3.—Shape of Spring for Armature.
P, Platinum foil. A A, Holes for screws to armature. H H, Holes for screws to support.
With a composite magnet, however, there is no earthly difficulty in getting it right, for you have only to connect the battery to two wires and join the other two, and if they don’t make the magnet work, join up one to the battery instead of one of those joined, and connect the other two wires; whichever gives the best result stick to. You must get all the silk or cotton off the wire, where you join them, and twist them over and over tightly together; if you can solder them, so much the better. Pull the wire tight and wind it on the reels until the place where it is joined is pulled tightly and not left in a loop, which would look untidy. Fig. 2 gives an idea of the magnet completed, and I have endeavored by means of the arrows to show how the wire is wound, they are supposed to give the direction of the top layer of wire in each case; of course either may be wound from the inside, so you must also consider that in this picture the outside coils are joined. The magnet having been thus constructed, we must now turn our attention to the vibrating hammer which is to beat the drum. To make this we want another piece of soft iron of about the same size as that forming the yoke of the magnet, say, 1? inch × ½ inch × ? inch. We shall then require a piece of brass spring about three inches long and half an inch broad. This is made of very thin springy brass, so as to make a spring which will move the armature quickly. One end of the spring should be tapered off as shown in Fig. 3, and at the point P in the figure a small piece of platinum foil (the real thing, not tin-foil, which I am sure is often sold in cheap apparatus instead of it,) should be fastened, by solder if possible.
Fig. 4.—Drum Hammer Put Together.
A, A bar of soft iron. B, Brass spring of contact breaker. C, Portion of brass spring bent outwards, the platinum foil is soldered on at the point C. S S, Screws holding spring to soft iron. Holes are made at the points H H to fasten spring to support. D, Bent wire fastened to soft iron armature. E, Wooden head of drumstick.
We now want a piece of rather stout brass wire bent into the shape shown in Fig. 4. It must be about four inches long, but its length will be determined by the size of the drum and the length of the magnet when it is all put together. At the end of this wire you must have a wooden knob (not brass, which doesn’t produce nearly so much noise). This you will have provided ready for you if you purchase the drum, as they will naturally supply drumsticks with it, and the head of one of these cut off and fastened to the end of the wire, by simply making a hole and sticking it in, will answer the purpose beautifully.
This wire has to be fastened to the soft iron armature, a simple way of doing which is to drill a hole the exact size and insert the end; it can then be soldered in. Or, if you cannot drill a hole, you can simply solder it on. The brass spring has the end bent outwards, as shown in Fig. 4, and is fastened to the soft iron armature by screws, as shown in the figure at S S, or simply soldered on. The point C is the end that is tapered off, and the platinum wire is fixed at that point; the spring should extend about 1¼ inch beyond the armature at the other end. Two holes are drilled in the spring at the points H H, through which screws are passed into the support. This support may be either a piece of iron ½ inch long, ¾ inch broad and ¾ inch thick, or a piece of wood will answer very well, and save drilling holes in the iron. If it is wood it had better be larger, say ¾ inch by ¾ inch by 1¼ inch.
PART IV.
We can now proceed to fasten all the parts together. We must have a piece of hard wood for the base, about 3½ inches by 3 inches and ? inch thick. On this the magnet has to be fastened by its support being screwed firmly down. In front of it the armature has to be fastened at such a height as to be exactly in front of the poles of the magnet. The relative positions of the parts are shown in Fig. 5, so I do not think a detailed account of their exact positions on the base is at all necessary.
There is, however, one piece of the mechanism in the figure to which I have introduced you, this is the contact-screw shown at C. To make this we take a piece of brass about 1½ inch long, ½ inch broad, and rather less than ? inch thick, and bend it at right angles, so that one leg is one inch long and the other ½ inch. Now in the part that is ½ inch have to be drilled three holes to fasten it with nails or screws to the base. The other part, one inch long, will then stand erect, but before fastening it in its place we put it to stand in front of the magnet and mark a point which is exactly on a level with the piece of platinum foil on the spring, when the spring and magnet are fixed in position. A hole has now to be drilled through that point and tapped to admit a brass screw with a milled head, and fix the piece in which the screw works to the front hole, so that the screw will work through it.
Fig. 5.—Interior Mechanism of Drum Complete.
M, Magnet. Y, Yoke of magnet. B, Brass support of magnet. A, Armature of soft iron attached to S, spring fastened to armature by screws at P, and to support by screws at H H. T, Support of spring. D, Head of drumstick. W, Wire supporting head of drumstick. C, Contact screw and support. The wire from one coil is joined to brass spring at H H. The wire X, coming from the other coil, and K, the wire from the contact-breaker, are joined to battery. Positions of screws joining parts together are shown by dotted lines. The side marked Z is placed at the bottom when fixing into the drum.
The point of the screw has now to be cut off and a very small piece of platinum wire fixed at the end. This wire will now come in contact with the platinum foil on the spring, when the brass support is fixed in a certain position on the base, and it is now to be fixed in that position with screws or nails. It should be so fixed that when the screw is turned till it is nearly out of its hole the wire is just out of contact with the platinum foil on the spring. It is now evident that by turning the screw one way you make the spring vibrate more rapidly, and by turning it the other way its efforts are relaxed.
The contact-breaker screw having been fixed in its place, and the support of the spring also fixed as at T in the diagram (Fig. 5)—by screws through the base into the iron, if it is made of iron, or by nails or screws through it into the base if of wood—all the parts are now together, and all that remains to be done is to make the necessary connections. One wire that comes from the magnet is to be joined (soldered, if possible,) to the spring at H in the picture; the other wire is left loose. To the brass support of the contact screw we solder another piece of wire. Now this piece of wire is connected with the zinc of the battery and the other (coming from the coil of the magnet) with the carbon of the battery. What happens?
The electricity passes along the wire X, we will say, and round the magnet coils, thus turning the cores into magnets. It then goes down the other wire to H, up the brass spring, along the screw, and down by the brass support to the other wire, by which it returns to the battery. That is to say, it would do all this if the armature stood still, but, of course, when the cores become magnets they attract the armature, which instantly moves towards them; this breaks the circuit, the spring moving off the platinum point of the screw, and the armature springs back again, which makes the circuit complete and the magnet attracts it again, and so on. The object of the spring is to get a good deal of vibration, and it and the screw should be so adjusted that although the armature is close enough to the magnet to make it certain to “go off” directly it is meant to do so, yet there may be as much scope for the spring to work with elasticity as possible.
We have now completed the electrical part of the business, but a slightly necessary part of the apparatus has yet to be obtained—viz., the drum. You can easily make a drum if you like, by taking a broad piece of tin, twisting it round to form a hoop, and covering the ends with parchment strained tightly over them. However, I should certainly not do so, for there can hardly be any spot, I should think, which boasts of a toy-shop at all, where drums cannot be procured! For twenty-five cents you can get a very superior drum, just about the right size; if you like to get a bigger one and make the mechanical part bigger, you will, of course, be rewarded by more noise.
Now, suppose you have got a 25-cent toy-drum, you must proceed to take off one end. If you look at the construction of the drum you will find (at least it is the case with my own, and I have not seen any that are differently made) that by cutting one of the double strings that fasten the wood hoops at the top and bottom together, and then loosening all the other strings with your fingers, the wooden hoop at one end will come right off, if the nails fastening the ends together are taken out, and that then the inner hoop on which the parchment is stretched will also come off and leave that side of the drum open.
Now, this is simply grand for our purpose, for when we have arranged our little dodges inside the drum, we can put on all the hoops again, replace the one double string, and no one will be an atom the wiser. If you could get off the side without breaking any strings it would save the trouble of replacing any, but I am afraid this is hardly possible. However, off comes the side of our drum, and what is to be done next? Well, the “beater” must be put bodily inside the drum, just so close to the parchment side that was taken off that the wooden head of the drumstick touches it when attracted by the magnet. You can easily find the right place in actual practice by setting the beater going and finding the spot inside the drum where it kicks up the worst racket when working. It must not be too close or it will hinder the vibration, and we want the hammer to go off instanter when required. The beater is fixed to the side of the drum with its side marked Z in the figure (5) downwards. It is easily fastened there by making two holes in the wood (in the thickness of it), and two corresponding holes in the metal side of the drum, and then screwing it down in its proper place.
Two holes are to be made in the side of the drum and two ornamental bits of silk-covered flexible copper conductor let through. They can be secured by simply tying knots inside the drum, and the copper ends are now to be fastened, one to the wire X and the other to the wire K from the contact screw support. Having done all this and made sure that the beater works when the ends of the flexible cord outside the drum are connected with the battery, we seal up our drum again, and that is then concluded.
Now as to fixing it up, I think I may fairly assume that you know how to make it work by an ordinary battery and a “press.” It is only necessary to run a double wire from battery to press and from press to drum, one wire of the double conductor being fastened to the carbon end of the battery and the other to the zinc end, and the other end of one wire to one of the wires coming from the drum. The other wire coming from the drum is then joined to the bottom conductor of the press, and the upper conductor of the press is joined to the other wire of the double conductor that goes to the battery. It is all very easy to understand if you follow the course of the current and consider that it has to pass through the drum and the press when the latter is pushed down, and be stopped when it is left to spring up again.
But the more magical arrangement can be made with the drum, and I think it is well worth while to do it, if merely for the fun of mystifying people. The drum is going to be suspended by the flexible cords; therefore, let them be the same length, and cutting off all the coverings at the end of each, fasten a brass “eye” to the copper, twisting the wire well round the bottom of the eye. Now wind silk of the same color as the rest all round the join, so that the connection of wire and eye is completely hidden, and the eye appears merely fastened to the flexible cord as a means of suspending the drum. Now we want to construct a hook from which the drum can be hung.
PART V.
Take two small pieces of brass wire about an inch long, and turn up the ends of each into a hook. Now get a minute piece of ebonite of the same length, and, putting one hook on one side and one on the other, bind the whole together with silk. If you cannot get ebonite easily you can use a small piece of sealing-wax in the same way; by heating the wires you can sink them into the wax and so make a neater join. Now the wires must not touch each other anywhere, but must be completely separated by the ebonite or sealing-wax. The double wire from the battery and press is now fastened, one wire to the press hook on one side, and one wire to that on the other side of the sealing-wax or ebonite. Wind silk over the whole to cover the joins, and a neat double hook is the result. The picture (Fig. 6) gives the method of making the hook, and it also gives a great deal more, which I now proceed to explain.
Supposing we can rig up a small beam of wood from which to suspend the drum, we can make matters more mysterious still. Let the double wire, being hidden by some means or other all along its course, be conducted on to the end of the beam. It can then be trained along the top of it until it comes to the point from which the drum is to hang. Here there must be a hole drilled, large enough to admit the hook rather tightly. Pull the double wire through and fasten the two wires to the hooks as before described.
Fig. 6.—Hook From Which to Suspend the Magic Drum.
W, Double wire from battery and “press.” B, Beam of wood from which drum is suspended. H H, Brass hooks at side. S, Ebonite or sealing-wax between the hooks. The beam is, of course, shown in section.
Now you can pull back the wire and fix the hook firmly in the hole, hiding the double wire at the top of the beam (of course if it is high up no one will be able to see over the top of the beam, so you will be quite safe); the hook being thus fixed will not attract any one’s notice, and look quite unsuspicious. The chief glory of the double hook thus constructed is, of course, that you can remove the drum whenever you choose, for examination, and whenever you hang it up you have only to hitch one eye over one side of the hook and the other over the other side, and the drum will work. People who are not up in the matter cannot conceive how the electricity can get to the drum, when it is simply hung by an (apparently) ordinary cord and ordinary eyes to what looks like an ordinary hook attached to a beam in a plain and straightforward manner.
You are now possessed of an electric trumpet and an electric drum, which you can put one at one end of the room and the other at the other. By running double wires from battery and press to the trumpet, and another double wire from battery and press to the drum, you can arrange matters so that when you put one press down the trumpet works, and when the other press is put down the drum works. If you want to work both together you must either have a very powerful battery (say 6 or 7 cells, No. 2 Lechlanche) or two batteries, one for trumpet and one for drum. If you want to use one battery for both you can make either work (at different times) from the same battery and presses, wherever they may be, by having a two-way switch in a dark corner of the wire.
Fig. 7.—Method of Joining Switch Drum and Trumpet to Press and Battery.
S, Switch. B, Battery. P, Press. D, Drum. T, Trumpet. The arrows show the course of the current when the switch is at A C and A G respectively.
It is very confusing business setting up the wires so as to produce the right effect, which is to change the current from drum to trumpet and vice versa in a moment by merely altering the handle of the switch. Readers who are not accustomed to the work will find it most intricate, and as I have done it myself several times, they may as well have the benefit of my trouble. I therefore give an illustration of how to connect up the wires (Fig. 7), and hope it will make matters clear to them. An explanation of the picture is necessary.
Suppose first of all that the switch is at A C, then the current will travel from the right-hand end of the battery, B, up one wire of the double conductor to the press, P, as shown by the lower arrow, through the press and along the wire, as shown by the top arrow, to the middle of the switch, A, down the arm of the switch to C, up one wire of the double conductor to the drum, and down by the other wire to the other end of the battery.
Now let the handle of the switch be moved to the other terminal, as shown by the dotted lines. The current will now go from the right-hand end of the battery to press and center of switch as before, it then goes down the arm of the switch up to the trumpet by the wire on the left side, and down to the other end of the battery by the wire on the right side, as shown by the arrows. Therefore when the arm of the switch is at A C the press will work the drum; when it is at A G the press will work the trumpet.
Suppose we have no press, but instead of it we have only one wire going straight from the right-hand end of the battery to the middle of the switch. Now let two incandescent lamps be substituted for the trumpet and drum. When the arm of the switch is at A C the current goes straight up from the right-hand pole of the battery to the center of the switch, along the arm, up to the lamp on the left-hand side, and down to the other pole of the battery. Now, suppose the arm of the switch is moved to A G, the current will go up as before to the center of the switch, down by the arm, up the wire to the lamp on the right-hand side, and back to the battery by the other wire. In the first case, therefore, the lamp at D lights up, in the second case the lamp at T lights up. The wires from C to D and G to T may be as long as you please, you can therefore control the lamps when they are far apart or in different parts of the house. When the arm of the switch is central neither lamp lights up, or, if you are fitting up the trumpet and drum, the press will not work either when the switch is in this position. This is an advantage, as when people get too inquisitive you can turn off the current, and then whatever they do they will not make the trumpet or drum work till you turn it on again, which you can do when you want them to work for you!
The construction of the switch is so simple that it is hardly necessary to explain the method of joining the wires, but I may say that one is to be joined to the bottom of the brass pillar in the center which supports the brass arm. The others are joined to the right and left terminals, generally by brass screws under the base, but sometimes by screw terminals at the upper surface; this depends on the make of switch which is purchased.
Ingenious readers can easily make a switch for themselves; it only requires a brass arm attached at one end to a central figure, and long enough to touch two screws, or pieces of brass, fixed to the base on opposite sides of it, when turned in their direction. The end of the arm not supported by the brass pillar is provided with a small wooden handle to turn it by.
The switch should be arranged to occupy some dark corner in which you can turn on drum or trumpet to work from the “presses” at will without any one seeing you alter it.
I will only add one thing in conclusion, and that is, that you can have the double wire from the battery and center of switch to the press at the end as long as you like, and it can turn about behind furniture or under the carpet as much as you like, and it will still work instantly from the end press.
Now, by scraping the wire clean at any intermediate point, or as many points as you like, and arranging a simple spring contact fastened to the wires without breaking them so that they can be made to touch when required and spring apart directly the touch is removed (this is easily done with two springs consisting of two strips of sheet brass, one fastened to one wire and one to the other, separated by a piece of wood except at the end when pressed together), you can make the trumpet squeak or the drum roll at any part of the room you like. The springs can be hidden under the carpet so as to be absolutely undiscernible except to the initiated. The best places are under furniture with rather long legs; the foot of the operator can then be placed on the springs, and so make them meet and the trumpet or drum sound without the least chance of detection. The wires not being broken in fixing the springs as described, those springs which are closer to the battery, in no way interfere with those which are further off, as, when these are used, the current simply runs round those that intervene between them and the battery, without being in any way hindered in its course, and the press at the end of the double wire will, therefore, work just as if no intermediate springs existed.
