Page:United States patent 586193.pdf/6
tuned plates, but this arrangement is not quite as satisfactory as the single tube. It is necessary when using tubes of the type I have described not to insert in the circuit more than 235one cell of the Leclanché type, as a higher electromotive force than 1.5 volts is apt to pass a current through the tube even when no oscillations are transmitted. I can, however, construct tubes capable of working with 240a much higher electromotive force. Fig. 6 shows one of these tubes. In this tube instead of one space or gap filled with filings there are several spaces separated by sections of tight-fitting silver wire. A tube thus 245constructed, observing also the rules of construction of any tubes in general, will work satisfactorily if the electromotive force of the battery in circuit with the tube is equal to 1.2 volts multiplied by the number of gaps. With 250this tube also it is well not to allow a current of more than one milliampere to pass.
The tube j may be replaced by other forms of imperfect electrical contacts, but this is not desirable.
255The plates k are of copper or aluminium or other metal, about half an inch or more broad, about one-fiftieth of an inch thick, and preferably of such a length as to be electrically tuned with the electric oscillations transmitted.260 The means I adopt for fixing the length of the plates is as follows: I stick a rectangular strip of tin-foil m (see Fig. 7) about twenty inches long (the length depends on the supposed length of wave that one is measuring)265 by means of a weak solution of gum onto a glass plate m2. Then by means of a very sharp penknife or point I cut across the middle of the tin foil, leaving a mark of division m2. If this detector is held in the proximity 270(four or five yards) and parallel with the axis of the oscillator in action, it will show little sparks at m2. If the length of the pieces of tin-foil approximates to the length of wave emitted from the oscillator, the spark will take 275place between them at a certain distance from the transmitter, which is a maximum when they are of suitable length. By shortening or lengthening the strips, therefore, it is easy to find the length most appropriate to the length 280of wave emitted by the oscillator. It is desirable to try this detector in the focus or focal line of the reflector. The length so found is the proper length for the plates k, or rather these should be about half an inch shorter on 285account of the length of the sensitive tube j, connected between them.
l is a cylindrical parabolic reflector similar to that used at the transmitting-station.
The plates k may be in the form of tubes or 290even wires.
It is slightly advantageous for the focal distance of the reflector to be equal to one-fourth or three-fourths of the wave length of the oscillation transmitted.
295When no oscillations are sent from the transmitting-station, the tube j does not conduct the current, and the local-battery circuit is broken, but when the powder or tube is influenced by the electrical oscillations from the transmitter it conducts and closes the circuit.300 I find, however, that when once started the powder in the tube continues to conduct even when the oscillations from the transmitter have ceased, but if it be shaken or tapped the circuit is broken. A tube well305 prepared will instantly interrupt the current passing through it at the slightest tap, provided it is inserted in a circuit in which there is little self-induction and small electromotive force, such as a single cell, and where the effects of310 self-induction have been removed by one of the methods which I will presently describe.
The two plates k communicate with the local circuit through two very small coils k1, which I will call “choking-coils,” formed by315 winding a few inches of very thin and insulated copper wire around a bit of iron wire about an inch and a half long. The object of these choking-coils is to prevent the high-frequency oscillation induced across these plates by the320 transmitter from dissipating itself by running along the local-battery wires which might weaken its effect on the sensitive tube j. These choking-coils may, however, be sometimes replaced by simple thin wires. They325 may also be connected directly to the tube j. The local circuit in which the sensitive tube j is inserted contains a sensitive relay n, preferably wound to a resistance of about twelve hundred ohms. This resistance need not be330 necessarily that of the relay, but may be the sum of the resistance of the relay and another additional resistance. The relay ought to be one possessing small self-induction.
The plates k, tube j, and coils k1 are 335fastened by means of wire stitches o1 to a thin glass tube o, preferably not longer than twelve inches, firmly fixed at one end to a strong piece of timber o2. This may be done by means of wood or ebonite grasping-screws.340
I do the tapping automatically by the current started by the tube, employing a trembler p on the circuit of the relay n similar in construction to that of an electric bell, but having a shorter arm. The vibrator must be345 carefully adjusted. Preferably the blows should be directed slightly upward to prevent the filings from getting caked. In place of tapping the tube the powder can be disturbed by slightly moving outward and inward one350 or both of the stops, the trembler p being replaced by a small electromagnet (or magnets) whose armature is connected to the stop.
I ordinarily work the telegraphic receiver h (or other instruments) by a derivation, as355 shown, from the circuit which works the trembler p. They can also, however, be worked in series with the trembler. When working ordinary sounders or Morse apparatus, a special adjustment of the same is sometimes360 needed to enable one to obtain dots and dashes. Sometimes it is necessary to work the telegraphic instruments or relays from the back-stops of the first relay, as is done in