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 princ.i.p.al 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 circ.u.mstances 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.

The applications of the microphone were soon of great importance. Dr. B.

W. Richardson succeeded in fitting it for auscultation of the heart and lungs; while Sir Henry Thompson has effectively used it in those surgical operations, such as probing wounds for bullets or fragments of bone, in which the surgeon has. .h.i.therto relied entirely on his delicacy of touch for detecting the jar of the probe on the foreign body.

There can be no doubt that in the science of physiology, in the art of surgery, and in many other walks of life, the microphone has proved a valuable aid.

Professor Hughes communicated his results to the Royal Society in the early part of 1878, and generously gave the microphone to the world. For his own sake it would perhaps have been better had he patented and thus protected it, for Mr. Edison, recognising it as a rival to his carbon-transmitter, then a valuable property, claimed it as an infringement of his patents and charged him with plagiarism. A spirited controversy arose, and several bitter lawsuits were the consequence, in none of which, however, Professor Hughes took part, as they were only commercial trials. It was clearly shown that Clerac, and not Edison, had been the first to utilise the variable resistance of powdered carbon or plumbage under pressure, a property on which the Edison transmitter was founded, and that Hughes had discovered a much wider principle, which embraced not only the so-called 'semi-conducting' bodies, such as carbon; but even the best conductors, such as gold, silver, and other metals. This principle was not a mere variation of electrical conductivity in a ma.s.s of material brought about by compression, but a mysterious variation in some unknown way of the strength of an electric current in traversing a loose joint or contact between two conductors.

This discovery of Hughes really shed a light on the behaviour of Edison's own transmitter, whose action he had until then misunderstood.

It was now seen that the particles of carbon dust in contact which formed the b.u.t.ton were a congeries of minute micro-phones. Again it was proved that the diaphragm or tympanum to receive the impression of the sound and convey it to the carbon b.u.t.ton, on which Edison had laid considerable stress, was non-essential; for the microphone, pure and simple, was operated by the direct impact of the sonorous waves, and required no tympanum. Moreover, the microphone, as its name implies, could magnify a feeble sound, and render audible the vibrations which would otherwise escape the ear. The discovery of these remarkable and subtle properties of a delicate contact had indeed confronted Edison; he had held them in his grasp, they had stared him in the face, but not-withstanding all his matchless ingenuity and ac.u.men, he, blinded perhaps by a false hypothesis, entirely failed to discern them. The significant proof of it lies in the fact that after the researches of Professor Hughes were published the carbon transmitter was promptly modified, and finally abandoned for practical work as a telephone, in favour of a variety of new transmitters, such as the Blake, now employed in the United Kingdom, in all of which the essential part is a microphone of hard carbon and metal. The b.u.t.ton of soot has vanished into the limbo of superseded inventions.

Science appears to show that every physical process is reciprocal, and may be reversed. With this principle in our minds, we need not be surprised that the microphone should not only act as a TRANSMITTER of sounds, but that it should also act as a RECEIVER. Mr. James Blyth, of Edinburgh, was the first to announce that he had heard sounds and even speech given out by a microphone itself when subst.i.tuted for the telephone. His transmitting microphone and his receiving one were simply jelly-cans filled with cinders from the grate. It then transpired that Professor Hughes had previously obtained the same remarkable effects from his ordinary 'pencil' microphones. The sounds were extremely feeble, however, but the transmitting microphones proved the best articulating ones. Professor Hughes at length constructed an adjustable hammer-and-anvil microphone of gas-carbon, fixed to the top of a resonating drum, which articulated fairly well, although not so perfectly as a Bell telephone. Perhaps a means of improving both the volume and distinctness of the articulation will yet be forthcoming and we may be able to speak solely by the microphone, if it is found desirable. The marvellous fact that a little piece of charcoal can, as it were, both listen and speak, that a person may talk to it so that his friend can hear him at a similar piece a hundred miles away, is a miracle of nineteenth century science which far transcends the oracles of antiquity.

The articulating telephone was the forerunner of the phonograph and microphone, and led to their discovery. They in turn will doubtless lead to other new inventions, which it is now impossible to foresee. We ask in vain for an answer to the question which is upon the lips of every one-What next? The microphone has proved itself highly useful in strengthening the sounds given out by the telephone, and it is probable that we shall soon see those three inventions working unitedly; for the microphone might make the telephone sounds so powerful as to enable them to be printed by phonograph as they are received, and thus a durable record of telephonic messages would be obtained. We can now transmit sound by wire, but it may yet be possible to transmit light, and see by telegraph. We are apparently on the eve of other wonderful inventions, and there are symptoms that before many years a great fundamental discovery will be made, which will elucidate the connection of all the physical forces, and will illumine the very frame-work of Nature.

In 1879, Professor Hughes endowed the scientific world with another beautiful apparatus, his 'induction balance.' Briefly described, it is an arrangement of coils whereby the currents inducted by a primary circuit in the secondary are opposed to each other until they balance, so that a telephone connected in the secondary circuit is quite silent.

Any disturbance of this delicate balance, however, say by the movement of a coil or a metallic body in the neighbourhood of the apparatus, will be at once reported by the induction currents in the telephone. Being sensitive to the presence of minute ma.s.ses of metal, the apparatus was applied by Professor Graham Bell to indicate the whereabouts of the missing bullet in the frame of President Garfield, as already mentioned, and also by Captain McEvoy to detect the position of submerged torpedoes or lost anchors. Professor Roberts-Austen, the Chemist to the Mint, has also employed it with success in a.n.a.lysing the purity and temper of coins; for, strange to say, the induction is affected as well by the molecular quality as the quant.i.ty of the disturbing metal. Professor Hughes himself has modified it for the purpose of sonometry, and the measurement of the hearing powers.

To the same year, 1879, belong his laborious investigations on current induction, and some ingenious plans for eliminating its effects on telegraph and telephone circuits.

Soon after his discovery of the microphone he was invited to become a Fellow of the Royal Society, and a few years later, in 1885 he received the Royal Medal of the Society for his experiments, and especially those of the microphone. In 1881 he represented the United Kingdom as a Commissioner at the Paris International Exhibition of Electricity, and was elected President of one of the sections of the International Congress of Electricians. In 1886 he filled the office of President of the Society of Telegraph Engineers and of Electricians.

The Hughes type-printer was a great mechanical invention, one of the greatest in telegraphic science, for every organ of it was new, and had to be fashioned out of chaos; an invention which stamped its author's name indelibly into the history of telegraphy, and procured for him a special fame; while the microphone is a discovery which places it on the roll of investigators, and at the same time brings it to the knowledge of the people. Two such achievements might well satisfy any scientific ambition. Professor Hughes has enjoyed a most successful career.

Probably no inventor ever before received so many honours, or bore them with greater modesty.

APPENDIX.

I. CHARLES FERDINAND GAUSS.

CHARLES FERDINAND GAUSS was born at Braunschweig on April 30, 1777. His father, George Dietrich, was a mason, who employed himself otherwise in the hard winter months, and finally became cashier to a TODTENCa.s.sE, or burial fund. His mother Dorothy was the daughter of Christian Benze of the village of Velpke, near Braunschweig, and a woman of talent, industry, and wit, which her son appears to have inherited. The father died in 1808 after his son had become distinguished. The mother lived to the age of ninety-seven, but became totally blind. She preserved her low Saxon dialect, her blue linen dress and simple country manners, to the last, while living beside her son at the Observatory of Gottingen.

Frederic, her younger brother, was a damask weaver, but a man with a natural turn for mathematics and mechanics.

When Gauss was a boy, his parents lived in a small house in the Wendengrahen, on a ca.n.a.l which joined the Ocker, a stream flowing through Braunschweig. The ca.n.a.l is now covered, and is the site of the Wilhelmstra.s.se, but a tablet marks the house. When a child, Gauss used to play on the bank of the ca.n.a.l, and falling in one day he was nearly drowned. He learned to read by asking the letters from his friends, and also by studying an old calendar which hung on a wall of his father's house, and when four years old he knew all the numbers on it, in spite of a shortness of sight which afflicted him to the end. On Sat.u.r.day nights his father paid his workmen their wages, and once the boy, who had been listening to his calculations, jumped up and told him that he was wrong. Revision showed that his son was right.

At the age of seven, Gauss went to the Catherine Parish School at Braunschweig, and remained at it for several years. The master's name was b.u.t.tner, and from a raised seat in the middle of the room, he kept order by means of a whip suspended at his side. A bigger boy, Bartels by name, used to cut quill pens, and a.s.sist the smaller boys in their lessons. He became a friend of Gauss, and would procure mathematical books, which they read together. Bartels subsequently rose to be a professor in the University of Dorpat, where he died. At the parish school the boys of fourteen to fifteen years were being examined in arithmetic one day, when Gauss stepped forward and, to the astonishment of b.u.t.tner, requested to be examined at the same time. b.u.t.tner, thinking to punish him for his audacity, put a 'poser' to him, and awaited the result. Gauss solved the problem on his slate, and laid it face downward on the table, crying 'Here it is,' according to the custom. At the end of an hour, during which the master paced up and down with an air of dignity, the slates were turned over, and the answer of Gauss was found to be correct while many of the rest were erroneous. b.u.t.tner praised him, and ordered a special book on arithmetic for him all the way from Hamburg.

From the parish school Gauss went to the Catherine Gymnasium, although his father doubted whether he could afford the money. Bartels had gone there before him, and they read the higher mathematics. Gauss also devoted much of his time to acquiring the ancient and modern languages.

From there he pa.s.sed to the Carolinean College in the spring of 1792.

Shortly before this the Duke Charles William Ferdinand of Braunschweig among others had noticed his talents, and promised to further his career.

In 1793 he published his first papers; and in the autumn of 1795 he entered the University of Gottingen. At this time he was hesitating between the pursuit of philology or mathematics; but his studies became more and more of the latter order. He discovered the division of the circle, a problem published in his DISQUISITIONES ARITHMETICAE, and henceforth elected for mathematics. The method of least squares, was also discovered during his first term. On arriving home the duke received him in the friendliest manner, and he was promoted to Helmstedt, where with the a.s.sistance of his patron he published his DISQUISITIONES.

On January 1, 1801, Piazzi, the astronomer of Palermo, discovered a small planet, which he named CERES FERDINANDIA, and communicated the news by post to Bode of Berlin, and Oriani of Milan. The letter was seventy-two days in going, and the planet by that time was lost in the glory of the sun, By a method of his own, published in his THEORIA MOTUS CORPORUM COELESTIUM, Gauss calculated the orbit of this planet, and showed that it moved between Mars and Jupiter. The planet, after eluding the search of several astronomers, was ultimately found again by Zach on December 7, 1801, and on January 1, 1802. The ellipse of Gauss was found to coincide with its...o...b..t.

This feat drew the attention of the Hanoverian Government, and of Dr. Olbers, the astronomer, to the young mathematician. But some time elapsed before he was fitted with a suitable appointment. The battle of Austerlitz had brought the country into danger, and the Duke of Braunschweig was entrusted with a mission from Berlin to the Court of St. Petersburg. The fame of Gauss had travelled there, but the duke resisted all attempts to bring or entice him to the university of that place. On his return home, however, he raised the salary of Gauss.

At the beginning of October 1806, the armies of Napoleon were moving towards the Saale, and ere the middle of the month the battles of Auerstadt and Jena were fought and lost. Duke Charles Ferdinand was mortally wounded, and taken back to Braunschweig. A deputation waited on the offended Emperor at Halle, and begged him to allow the aged duke to die in his own house. They were brutally denied by the Emperor, and returned to Braunschweig to try and save the unhappy duke from imprisonment. One evening in the late autumn, Gauss, who lived in the Steinweg (or Causeway), saw an invalid carriage drive slowly out of the castle garden towards the Wendenthor. It contained the wounded duke on his way to Altona, where he died on November 10, 1806, in a small house at Ottensen, 'You will take care,' wrote Zach to Gauss, in 1803, 'that his great name shall also be written on the firmament.'

For a year and a half after the death of the duke Gauss continued in Braunschweig, but his small allowance, and the absence of scientific company made a change desirable. Through Olbers and Heeren he received a call to the directorate of Gottingen University in 1807, and at once accepted it. He took a house near the chemical laboratory, to which he brought his wife and family. The building of the observatory, delayed for want of funds, was finished in 1816, and a year or two later it was fully equipped with instruments.

In 1819, Gauss measured a degree of lat.i.tude between Gottingen and Altona. In geodesy he invented the heliotrope, by which the sunlight reflected from a mirror is used as a "sight" for the theodolite at a great distance. Through Professor William Weber he was introduced to the science of electro-magnetism, and they devised an experimental telegraph, chiefly for sending time signals, between the Observatory and the Physical Cabinet of the University. The mirror receiving instrument employed was the heavy prototype of the delicate reflecting galvanometer of Sir William Thomson. In 1834 messages were transmitted through the line in presence of H.R.H. the Duke of Cambridge; but it was hardly fitted for general use. In 1883 (?) he published an absolute system of magnetic measurements.

On July 16, 1849, the jubilee of Gauss was celebrated at the University; the famous Jacobi, Miller of Cambridge, and others, taking part in it.

After this he completed several works already begun, read a great deal of German and foreign literature, and visited the Museum daily between eleven and one o'clock.

In the winters of 1854-5 Gauss complained of his declining health, and on the morning of February 23, 1855, about five minutes past one o'clock, he breathed his last. He was laid on a bed of laurels, and buried by his friends. A granite pillar marks his resting-place at Gottingen.

II. WILLIAM EDWARD WEBER.

WILLIAM EDWARD WEBER was born on October 24, 1804, at Wittenberg, where his father, Michael Weber, was professor of theology. William was the second of three brothers, all of whom were distinguished by an apt.i.tude for the study of science. After the dissolution of the University of Wittenberg his father was transferred to Halle in 1815. William had received his first lessons from his father, but was now sent to the Orphan Asylum and Grammar School at Halle. After that he entered the University, and devoted himself to natural philosophy. He distinguished himself so much in his cla.s.ses, and by original work, that after taking his degree of Doctor and becoming a Privat-Docent he was appointed Professor Extraordinary of natural philosophy at Halle.

In 1831, on the recommendation of Gauss, he was called to Gottingen as professor of physics, although but twenty-seven years of age. His lectures were interesting, instructive, and suggestive. Weber thought that, in order to thoroughly understand physics and apply it to daily life, mere lectures, though ill.u.s.trated by experiments, were insufficient, and he encouraged his students to experiment themselves, free of charge, in the college laboratory. As a student of twenty years he, with his brother, Ernest Henry Weber, Professor of Anatomy at Leipsic, had written a book on the 'Wave Theory and Fluidity,' which brought its authors a considerable reputation. Acoustics was a favourite science of his, and he published numerous papers upon it in Poggendorff's ANNALEN, Schweigger's JAHRBUCHER FUR CHEMIE UND PHYSIC, and the musical journal CAECILIA. The 'mechanism of walking in mankind'

was another study, undertaken in conjunction with his younger brother, Edward Weber. These important investigations were published between the years 1825 and 1838.

Displaced by the Hanoverian Government for his liberal opinions in politics Weber travelled for a time, visiting England, among other countries, and became professor of physics in Leipsic from 1843 to 1849, when he was reinstalled at Gottingen. One of his most important works was the ATLAS DES ERDMAGNETISMUS, a series of magnetic maps, and it was chiefly through his efforts that magnetic observatories were inst.i.tuted. He studied magnetism with Gauss, and in 1864 published his 'Electrodynamic Proportional Measures' containing a system of absolute measurements for electric currents, which forms the basis of those in use. Weber died at Gottingen on June 23, 1891.

III. SIR WILLIAM FOTHERGILL COOKE.

WILLIAM Fothergill Cooke was born near Ealing on May 4, 1806, and was a son of Dr. William Cooke, a doctor of medicine, and professor of anatomy at the University of Durham. The boy was educated at a school in Durham, and at the University of Edinburgh. In 1826 he joined the East India Army, and held several staff appointments. While in the Madras Native Infantry, he returned home on furlough, owing to ill-health, and afterwards relinquished this connection. In 1833-4 he studied anatomy and physiology in Paris, acquiring great skill at modelling dissections in coloured wax.

In the summer of 1835, while touring in Switzerland with his parents, he visited Heidelberg, and was induced by Professor Tiedeman, director of the Anatomical Inst.i.tute, to return there and continue his wax modelling. He lodged at 97, Stockstra.s.se, in the house of a brewer, and modelled in a room nearly opposite. Some of his models have been preserved in the Anatomical Museum at Heidelberg. In March 1836, hearing accidentally from Mr. J. W. R. Hoppner, a son of Lord Byron's friend, that the Professor of Natural Philosophy in the University, Geheime Hofrath Moncke had a model of Baron Schilling's telegraph, Cooke went to see it on March 6, in the Professor's lecture room, an upper storey of an old convent of Dominicans, where he also lived. Struck by what he witnessed, he abandoned his medical studies, and resolved to apply all his energies to the introduction of the telegraph. Within three weeks he had made, partly at Heidelberg, and partly at Frankfort, his first galvanometer, or needle telegraph. It consisted of three magnetic needles surrounded by multiplying coils, and actuated by three separate circuits of six wires. The movements of the needles under the action of the currents produced twenty-six different signals corresponding to the letters of the alphabet.

'Whilst completing the model of my original plan,' he wrote to his mother on April 5, 'others on entirely fresh systems suggested themselves, and I have at length succeeded in combining the UTILE of each, but the mechanism requires a more delicate hand than mine to execute, or rather instruments which I do not possess. These I can readily have made for me in London, and by the aid of a lathe I shall be able to adapt the several parts, which I shall have made by different mechanicians for secrecy's sake. Should I succeed, it may be the means of putting some hundreds of pounds in my pocket. As it is a subject on which I was profoundly ignorant, until my attention was casually attracted to it the other day, I do not know what others may have done in the same way; this can best be learned in London.'

The 'fresh systems' referred to was his 'mechanical' telegraph, consisting of two letter dials, working synchronously, and on which particular letters of the message were indicated by means of an electro-magnet and detent. Before the end of March he invented the clock-work alarm, in which an electro-magnet attracted an armature of soft iron, and thus withdrew a detent, allowing the works to strike the alarm. This idea was suggested to him on March 17, 1836, while reading Mrs. Mary Somerville's 'Connexion of the Physical Sciences,' in travelling from Heidelberg to Frankfort.

Cooke arrived in London on April 22, and wrote a pamphlet setting forth his plans for the establishment of an electric telegraph; but it was never published. According to his own account he also gave considerable attention to the escapement principle, or step by step movement, afterwards perfected by Wheatstone. While busy in preparing his apparatus for exhibition, part of which was made by a clock-maker in Clerkenwell, he consulted Faraday about the construction of electro-magnets, The philosopher saw his apparatus and expressed his opinion that the 'principle was perfectly correct,' and that the 'instrument appears perfectly adapted to its intended uses.'

Nevertheless he was not very sanguine of making it a commercial success.

'The electro-magnetic telegraph shall not ruin me,' he wrote to his mother, 'but will hardly make my fortune.' He was desirous of taking a partner in the work, and went to Liverpool in order to meet some gentleman likely to forward his views, and endeavoured to get his instrument adopted on the incline of the tunnel at Liverpool; but it gave sixty signals, and was deemed too complicated by the directors.

Soon after his return to London, by the end of April, he had two simpler instruments in working order. All these preparations had already cost him nearly four hundred pounds.

On February 27, Cooke, being dissatisfied with an experiment on a mile of wire, consulted Faraday and Dr. Roget as to the action of a current on an electro-magnet in circuit with a long wire. Dr. Roget sent him to Wheatstone, where to his dismay he learned that Wheatstone had been employed for months on the construction of a telegraph for practical purposes. The end of their conferences was that a partnership in the undertaking was proposed by Cooke, and ultimately accepted by Wheatstone. The latter had given Cooke fresh hopes of success when he was worn and discouraged. 'In truth,' he wrote in a letter, after his first interview with the Professor, 'I had given the telegraph up since Thursday evening, and only sought proofs of my being right to do so ere announcing it to you. This day's enquiries partly revives my hopes, but I am far from sanguine. The scientific men know little or nothing absolute on the subject: Wheatstone is the only man near the mark.'

It would appear that the current, reduced in strength by its pa.s.sage through a long wire, had failed to excite his electro-magnet, and he was ignorant of the reason. Wheatstone by his knowledge of Ohm's law and the electro-magnet was probably able to enlighten him. It is clear that Cooke had made considerable progress with his inventions before he met Wheatstone; he possessed a needle telegraph like Wheatstone, an alarm, and a chronometric dial telegraph, which at all events are a proof that he himself was an inventor, and that he doubtless bore a part in the production of the Cooke and Wheatstone apparatus. Contrary to a statement of Wheatstone, it appears from a letter of Cooke dated March 4, 1837, that Wheatstone 'handsomely acknowledged the advantage' of Cooke's apparatus had it worked;' his (Wheatstone's) are ingenious, but not practicable.' But these conflicting accounts are reconciled by the fact that Cooke's electro-magnetic telegraph would not work, and Wheatstone told him so, because he knew the magnet was not strong enough when the current had to traverse a long circuit.