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 ⅝ inch broad and ⅛ 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 ⅜ 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 1⅛ inch long, ½ inch broad, and ⅛ 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 ⅛ 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 ⅞ 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 1⅛ inch broad or ⅜ 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, 1⅜ inch × ½ inch × ⅛ 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.