In 1875, Professor Hughes introduced the type-printer into Spain, where he was made a Commander of the Royal and Distinguished Order of Carlos III. In every country to which it was taken, the merits of the instrument were recognised, and Professor Hughes has none but pleasant souvenirs of his visits abroad.
During all these years the inventor was not idle. He was constantly improving his invention; and in addition to that, he had to act as an instructor where-ever he went, and give courses of lectures explaining the principles and practice of his apparatus to the various employees into whose hands it was to be consigned.
The years 1876-8 will be distinguished in the history of our time for a triad of great inventions which, so to speak, were hanging together. We have already seen how the telephone and phonograph have originated; and to these two marvellous contrivances we have now to add a third, the microphone, which is even more marvellous, because, although in form it is the simplest of them all, in its action it is still a mystery. The telephone enables us to speak to distances far beyond the reach of eye or ear, 'to waft a sigh from Indus to the Pole; 'the phonograph enables us to seal the living speech on brazen tablets, and store it up for any length of time; while it is the peculiar function of the microphone to let us hear those minute sounds which are below the range of our unassisted powers of hearing. By these three instruments we have thus received a remarkable extension of the capacity of the human ear, and a growth of dominion over the sounds of Nature. We have now a command over sound such as we have over light. For the telephone is to the ear what the telescope is to the eye, the phonograph is for sound what the photograph is for light, and the microphone finds its analogue in the microscope. As the microscope reveals to our wondering sight the rich meshes of creation, so the microphone can interpret to our ears the jarr of molecular vibrations for ever going on around us, perchance the clash of atoms as they shape themselves into crystals, the murmurous ripple of the sap in trees, which Humboldt fancied to make a continuous music in the ears of the tiniest insects, the fall of pollen dust on flowers and grasses, the stealthy creeping of a spider upon his silken web, and even the piping of a pair of love-sick butterflies, or the trumpeting of a bellicose gnat, like the 'horns of elf-land faintly blowing.'
The success of the Hughes type-printer may be said to have covered its author with titles and scientific honours, and placed him above the necessity of regular employment. He left America, and travelled from place to place. For many years past, however, he has resided privately in London, an eminent example of that modesty and simplicity which is generally said to accompany true genius.
Mechanical invention is influenced to a very high degree by external circumstances. It may sound sensational, but it is nevertheless true, that we owe the microphone to an attack of bronchitis. During the thick foggy weather of November 1877, Professor Hughes was confined to his home by a severe cold, and in order to divert his thoughts he began to amuse himself with a speaking telephone. Then it occurred to him that there might be some means found of making the wire of the telephone circuit speak of itself without the need of telephones at all, or at least without the need of one telephone, namely, that used in transmitting the sounds. The distinguished physicist Sir William Thomson, had lately discovered the peculiar fact that when a current of electricity is passed through a wire, the current augments when the wire is extended, and diminishes when the wire is compressed, because in the former case the resistance of the material of the wire to the passage of the current is lessened, and in the latter case it becomes greater.
Now it occurred to Professor Hughes that, if this were so, it might be possible to cause the air-vibrations of sound to so act upon a wire conveying a current as to stretch and contract it in sympathy with themselves, so that the sound-waves would create corresponding electric waves in the current, and these electric waves, passed through a telephone connected to the wire, would cause the telephone to give forth the original sounds. He first set about trying the effect of vibrating a wire in which a current flowed, to see if the stretching and compressing thereby produced would affect the current so as to cause sounds in a telephone connected up in circuit with the wire--but without effect. He could hear no sound whatever in the telephone. Then he stretched the wire till it broke altogether, and as the metal began to rupture he heard a distinct grating in the telephone, followed by a sharp 'click,' when the wire sundered, which indicated a 'rush' of electricity through the telephone. This pointed out to him that the wire might be sensitive to sound when in a state of fracture. Acting on the hint, he placed the two broken ends of the wire together again, and kept them so by the application of a definite pressure. To his joy he found that he had discovered what he had been in search of. The imperfect contact between the broken ends of the wire proved itself to be a means of transmitting sounds, and in addition it was found to possess a faculty which he had not anticipated--it proved to be sensitive to very minute sounds, and was in fact a rude microphone. Continuing his researches, he soon found that he had discovered a prin- ciple of wide application, and that it was not necessary to confine his experiments to wires, since any substance which conducted an electric current would answer the purpose. All that was necessary was that the materials employed should be in contact with each other under a slight but definite pressure, and, for the continuance of the effects, that the materials should not oxidise in air so as to foul the contact. For different materials a different degree of pressure gives the best results, and for different sounds to be transmitted a different degree of pressure is required. Any loose, crazy unstable structure, of conducting bodies, inserted in a telephone circuit, will act as a microphone. Such, for example, as a glass tube filled with lead-shot or black oxide of iron, or 'white bronze' powder under pressure; a metal watch-chain piled in a heap. Surfaces of platinum, gold, or even iron, pressed lightly together give excellent results. Three French nails, two parallel beneath and one laid across them, or better still a log- hut of French nails, make a perfect transmitter of audible sounds, and a good microphone. Because of its cheapness, its conducting power, and its non-oxidisability, carbon is the most select material. A piece of charcoal no bigger than a pin's head is quite sufficient to produce articulate speech. Gas-carbon operates admirably, but the best carbon is that known as willow-charcoal, used by artists in sketching, and when this is impregnated with minute globules of mercury by heating it white- hot and quenching it in liquid mercury, it is in a highly sensitive microphonic condition. The same kind of charcoal permeated by platinum, tin, zinc, or other unoxidisable metal is also very suitable; and it is a significant fact that the most resonant woods, such as pine, poplar, and willow, yield the charcoals best adapted for the microphone. Professor Hughes' experimental apparatus is of an amusingly simple description. He has no laboratory at home, and all his experiments were made in the drawing-room. His first microphones were formed of bits of carbon and scraps of metal, mounted on slips of match-boxes by means of sealing-wax; and the resonance pipes on which they were placed to reinforce the effect of minute sounds, were nothing more than children's toy money boxes, price one halfpenny, having one of the ends knocked out. With such childish and worthless materials he has conquered Nature in her strongholds, and shown how great discoveries can be made. The microphone is a striking illustration of the truth that in science any phenomenon whatever may be rendered useful. The trouble of one generation of scientists may be turned to the honour and service of the next. Electricians have long had sore reasons for regarding a 'bad contact' as an unmitigated nuisance, the instrument of the evil one, with no conceivable good in it, and no conceivable purpose except to annoy and tempt them into wickedness and an expression of hearty but ignominious emotion. Professor Hughes, however, has with a wizard's power transformed this electrician's bane into a professional glory and a public boon. Verily there is a soul of virtue in things evil.
The commonest and at the same time one of the most sensitive forms of the instrument is called the 'pencil microphone,' from the pencil or crayon of carbon which forms the principal part of it. This pencil may be of mercurialised charcoal, but the ordinary gas-carbon, which incrusts the interior of the retorts in gas-works, is usually employed. The crayon is supported in an upright position by two little brackets of carbon, hollowed out so as to receive the pointed ends in shallow cups. The weight of the crayon suffices to give the required pressure on the contacts, both upper and lower, for the upper end of the Pencil should lean against the inner wall of the cup in the upper bracket. The brackets are fixed to an upright board of light, dry, resonant pine- wood, let into a solid base of the same timber. The baseboard is with advantage borne by four rounded india-rubber feet, which insulate it from the table on which it may be placed. To connect the microphone up for use, a small voltaic battery, say three cells (though a single cell will give surprising results), and a Bell speaking telephone are necessary. A wire is led from one of the carbon brackets to one pole of the battery, and another wire is led from the other bracket to one terminal screw of the telephone, and the circuit is completed by a wire from the other terminal of the telephone to the other pole of the battery. If now the slightest mechanical jar be given to the wooden frame of the microphone, to the table, or even to the walls of the room in which the experiment takes place, a corresponding noise will be heard in the microphone. By this delicate arrangement we can play the eavesdropper on those insensible vibrations in the midst of which we exist. If a feather or a camel-hair pencil be stroked along the base- board, we hear a harsh grating sound; if a pin be laid upon it, we hear a blow like a blacksmith's hammer; and, more astonishing than all, if a fly walk across it we hear it tramping like a charger, and even its peculiar cry, which has been likened, with some allowance for imagination, to the snorting of an elephant. Moreover it should not be forgotten that the wires connecting up the telephone may be lengthened to any desired extent, so that, in the words of Professor Hughes, 'the beating of a pulse, the tick of a watch, the tramp of a fly can then be heard at least a hundred miles from the source of sound.' If we whisper or speak distinctly in a monotone to the pencil, our words will be heard in the telephone; but with this defect, that the TIMBRE or quality is, in this particular form of the instrument, apt to be lost, making it difficult to recognise the speaker's voice. But although a single pencil microphone will under favourable circumstances transmit these varied sounds, the best effect for each kind of sound is obtained by one specially adjusted. There is one pressure best adapted for minute sounds, another for speech, and a third for louder sounds. A simple spring arrangement for adjusting the pressure of the contacts is therefore an advantage, and it can easily be applied to a microphone formed of a small rod of carbon pivoted at its middle, with one end resting on a block or anvil of carbon underneath. The contact between the rod and the block in this 'hammer-and-anvil' form is, of course, the portion which is sensitive to sound.
The microphone is a discovery as well as an invention, and the true explanation of its action is as yet merely an hypothesis. It is supposed that the vibrations put the carbons in a tremor and cause them to approach more or less nearly, thus closing or opening the breach between them, which is, as it were, the floodgate of the current.