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.