Edison, His Life and Inventions [78]
since died away, is suggestive of the difficulties involved in trying to do justice to everybody. A standard history describes the microphone thus:
"A form of apparatus produced during the early days of the telephone by Professor Hughes, of England, for the purpose of rendering faint, indistinct sounds distinctly audible, depended for its operation on the changes that result in the resistance of loose contacts. This apparatus was called the microphone, and was in reality but one of the many forms that it is possible to give to the telephone transmitter. For example, the Edison granular transmitter was a variety of microphone, as was also Edison's transmitter, in which the solid button of carbon was employed. Indeed, even the platinum point, which in the early form of the Reis transmitter pressed against the platinum contact cemented to the centre of the diaphragm, was a microphone."
At a time when most people were amazed at the idea of hearing, with the aid of a "microphone," a fly walk at a distance of many miles, the priority of invention of such a device was hotly disputed. Yet without desiring to take anything from the credit of the brilliant American, Hughes, whose telegraphic apparatus is still in use all over Europe, it may be pointed out that this passage gives Edison the attribution of at least two original forms of which those suggested by Hughes were mere variations and modifications. With regard to this matter, Mr. Edison himself remarks: "After I sent one of my men over to London especially, to show Preece the carbon transmitter, and where Hughes first saw it, and heard it--then within a month he came out with the microphone, without any acknowledgment whatever. Published dates will show that Hughes came along after me."
There have been other ways also in which Edison has utilized the peculiar property that carbon possesses of altering its resistance to the passage of current, according to the pressure to which it is subjected, whether at the surface, or through closer union of the mass. A loose road with a few inches of dust or pebbles on it offers appreciable resistance to the wheels of vehicles travelling over it; but if the surface is kept hard and smooth the effect is quite different. In the same way carbon, whether solid or in the shape of finely divided powder, offers a high resistance to the passage of electricity; but if the carbon is squeezed together the conditions change, with less resistance to electricity in the circuit. For his quadruplex system, Mr. Edison utilized this fact in the construction of a rheostat or resistance box. It consists of a series of silk disks saturated with a sizing of plumbago and well dried. The disks are compressed by means of an adjustable screw; and in this manner the resistance of a circuit can be varied over a wide range.
In like manner Edison developed a "pressure" or carbon relay, adapted to the transference of signals of variable strength from one circuit to another. An ordinary relay consists of an electromagnet inserted in the main line for telegraphing, which brings a local battery and sounder circuit into play, reproducing in the local circuit the signals sent over the main line. The relay is adjusted to the weaker currents likely to be received, but the signals reproduced on the sounder by the agency of the relay are, of course, all of equal strength, as they depend upon the local battery, which has only this steady work to perform. In cases where it is desirable to reproduce the signals in the local circuit with the same variations in strength as they are received by the relay, the Edison carbon pressure relay does the work. The poles of the electromagnet in the local circuit are hollowed out and filled up with carbon disks or powdered plumbago. The armature and the carbon-tipped poles of the electromagnet form part of the local circuit; and if the relay is actuated by a weak current the armature will be attracted but feebly. The carbon being only slightly compressed will offer considerable resistance to the flow of current from the local battery,
"A form of apparatus produced during the early days of the telephone by Professor Hughes, of England, for the purpose of rendering faint, indistinct sounds distinctly audible, depended for its operation on the changes that result in the resistance of loose contacts. This apparatus was called the microphone, and was in reality but one of the many forms that it is possible to give to the telephone transmitter. For example, the Edison granular transmitter was a variety of microphone, as was also Edison's transmitter, in which the solid button of carbon was employed. Indeed, even the platinum point, which in the early form of the Reis transmitter pressed against the platinum contact cemented to the centre of the diaphragm, was a microphone."
At a time when most people were amazed at the idea of hearing, with the aid of a "microphone," a fly walk at a distance of many miles, the priority of invention of such a device was hotly disputed. Yet without desiring to take anything from the credit of the brilliant American, Hughes, whose telegraphic apparatus is still in use all over Europe, it may be pointed out that this passage gives Edison the attribution of at least two original forms of which those suggested by Hughes were mere variations and modifications. With regard to this matter, Mr. Edison himself remarks: "After I sent one of my men over to London especially, to show Preece the carbon transmitter, and where Hughes first saw it, and heard it--then within a month he came out with the microphone, without any acknowledgment whatever. Published dates will show that Hughes came along after me."
There have been other ways also in which Edison has utilized the peculiar property that carbon possesses of altering its resistance to the passage of current, according to the pressure to which it is subjected, whether at the surface, or through closer union of the mass. A loose road with a few inches of dust or pebbles on it offers appreciable resistance to the wheels of vehicles travelling over it; but if the surface is kept hard and smooth the effect is quite different. In the same way carbon, whether solid or in the shape of finely divided powder, offers a high resistance to the passage of electricity; but if the carbon is squeezed together the conditions change, with less resistance to electricity in the circuit. For his quadruplex system, Mr. Edison utilized this fact in the construction of a rheostat or resistance box. It consists of a series of silk disks saturated with a sizing of plumbago and well dried. The disks are compressed by means of an adjustable screw; and in this manner the resistance of a circuit can be varied over a wide range.
In like manner Edison developed a "pressure" or carbon relay, adapted to the transference of signals of variable strength from one circuit to another. An ordinary relay consists of an electromagnet inserted in the main line for telegraphing, which brings a local battery and sounder circuit into play, reproducing in the local circuit the signals sent over the main line. The relay is adjusted to the weaker currents likely to be received, but the signals reproduced on the sounder by the agency of the relay are, of course, all of equal strength, as they depend upon the local battery, which has only this steady work to perform. In cases where it is desirable to reproduce the signals in the local circuit with the same variations in strength as they are received by the relay, the Edison carbon pressure relay does the work. The poles of the electromagnet in the local circuit are hollowed out and filled up with carbon disks or powdered plumbago. The armature and the carbon-tipped poles of the electromagnet form part of the local circuit; and if the relay is actuated by a weak current the armature will be attracted but feebly. The carbon being only slightly compressed will offer considerable resistance to the flow of current from the local battery,