In such cases it is usual to employ a local battery to produce the signals, and to close the local battery circuit by means of a relay working.
It will be observed that the circuit is not in this case actually open; the meaning of the expression " open circuit " is " no battery to line."
- Wireless Telegraphy The early attempts to achieve electric telegraphy involved the use of a complete metallic circuit, but K.
Under these circumstances a small portion of the current from the battery is shunted through the galvanometer circuit, and can be used to make electric signals.
The judicial power is vested in the Supreme Court of Appeals, the Circuit courts, such inferior courts as may be established, county courts, the powers and duties of which are, however, chiefly police and fiscal, and in justices of the peace.
In order to relieve the circuit judges the legislature has established by special acts inferior courts, generally with criminal jurisdiction only, in nine counties of the state.
The old ramparts and bastions (excluding the circuit of the citadel of 1591, now in great part demolished, in the south-east) make an enceinte of about 41 m., but the enclosed area is not all occupied by streets and houses.
Now, we know that the number of electrochemical equivalents electrolysed is proportional to the whole amount of electricity which passed through the circuit, and the product of this by the electromotive force of the battery is the work done by the latter, so that in this case also Joule showed that the heat generated was proportional to the work done.
For the longest circuit to be worked, the shorter circuits being brought up approximately to a level, as regards resistance, by the insertion of resistance coils in the circuit of the transmitting apparatus of each shorter line.
The arrangement on the " open-circuit " system for single-current working is shown in fig.
When signals are to be sent from either station the operator turns the switch c out of contact with the stop b, and then operates precisely as in open circuit send '" i ing.
Circuit-closing apparatus called a relay, which is practi cally an electromagnetic key which has its lever attached to the armature of the magnet and which can be worked by a very weak current.
It consists in punching, by means of " a puncher," a series of holes in a strip of paper in such a way that, when the strip is sent through another instrument, called the " transmitter," the holes cause the circuit to be closed at the proper times and for the proper proportionate intervals for the message to be correctly printed by the receiving instrument or recorder.
At the receiving end there are two telephone receivers, one joined in the loop circuit, the other in the earth return circuit.
The current thus sent to the line may be made either to act directly on the printing instrument or to close a local circuit by means of a relay.
This machine reproduces a copy of the original transmitting slip, which can be passed on to any other Wheatstone circuit or can be run through a " Creed printer," which is a pneumatic machine actuating a typewriter by means of valves.
Since each letter is represented by a specific combination of positive and negative currents, it is possible, by means of the combinations, to close a local circuit at any given interval, and so cause the paper to be pressed against the periphery of the type-wheel at the time when the letter required is opposite.
In the receiver there is a strong electromagnet, excited by a local current, which has in its circuit two annular air gaps, across which the magnetic field is practically uniform and constant.
Two receiving instruments, a siphon recorder and a mirror galvanometer, are shown; one only is absolutely necessary, but it is convenient Cable to have the galvanometer ready, so that in case of accident to the recorder it may be at once switched into circuit by the switch s.
Ance coil of some 2000 turns of insulated copper wire, enclosed in a laminated iron circuit, and connected at intervals to a number of terminals so that equal increments of inductance may be obtained.
Encouraged by this success, he even made the further suggestion that the remaining metallic portion of the circuit might perhaps some day be abolished and a system of wireless telegraphy established.'
Hence, by inserting a break-and-make key in the circuit of the battery, coil or dynamo, the uniform noise or hum in the telephone can be cut up into periods of long and short noises, which can be made to yield the signals of the Morse alphabet.
- Open Circuit, Single- (not in Great Britain).
It differs from the open circuit in only requiring one battery (although, as in the figure, half of it is often placed at each end), in having the re circuit ceiving instrument between the line and the key, and in having the battery continuously to the line.
This slip is then passed through a transmitter fitted with brush contacts and connected to the two line wires of a metallic loop. One circuit is formed by the loop itself, and a second, quite independent, by the two wires in parallel, earthed at each end.
At the receiving end of the circuit a shaft is coupled to the motor; this is provided with gearing which rotates four combining commutators and four type-wheels, which print the letters on the band of paper.