heroes of the telegraph-第37章
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g against one the voice is conveyed through the string； solely by mechanical vibration； to the other。 Gray employed electricity； and varied the strength of the current in conformity with the voice by causing the diaphragm in vibrating to dip a metal probe attached to its centre more or less deep into a well of conducting liquid in circuit with the line。 As the current passed from the probe through the liquid to the line a greater or less thickness of liquid intervened as the probe vibrated up and down； and thus the strength of the current was regulated by the resistance offered to the passage of the current。 His receiver was an electro…magnet having an iron plate as an armature capable of vibrating under the attractions of the varying current。 But Gray allowed his idea to slumber； whereas Bell continued to perfect his apparatus。 However； when Bell achieved an unmistakable success； Gray brought a suit against him； which resulted in a compromise； one public company acquiring both patents。
Bell's invention has been contested over and over again； and more than one claimant for the honour and reward of being the original inventor of the telephone have appeared。 The most interesting case was that of Signor Antonio Meucci； an Italian emigrant； who produced a mass of evidence to show that in 1849； while in Havanna； Cuba； he experimented with the view of transmitting speech by the electric current。 He continued his researches in 1852…3； and subsequently at Staten Island； U。S。； and in 1860 deputed a friend visiting Europe to interest people in his invention。 In 1871 he filed a caveat in the United States Patent Office； and tried to get Mr。 Grant； President of the New York District Telegraph Company； to give the apparatus a trial。 Ill…health and poverty； consequent on an injury due to an explosion on board the Staten Island ferry boat Westfield； retarded his experiments； and prevented him from completing his patent。 Meucci's experimental apparatus was exhibited at the Philadelphia Exhibition of 1884； and attracted much attention。 But the evidence he adduces in support of His early claims is that of persons ignorant of electrical science； and the model shown was not complete。 The caveat of 1871 is indeed a reliable document； but unfortunately for him it is not quite clear from it whether he employed a 'lovers' telephone；' with a wire instead of a string； and joined a battery to it in the hope of enhancing the effect。 'I employ；' he says； 'the well known conducting effect of continuous metallic conductors as a medium for sound； and increase the effect by electrically insulating both the conductor and the parties who are communicating。 It forms a speaking telegraph without the necessity of any hollow tube。' In connection with the telephone he used an electric alarm。 It is by no means evident from this description that Meucci had devised a practicable speaking telephone； but he may have been the first to employ electricity in connection with the transmission of speech。 ＇Meucci is dead。＇
'This crowning marvel of the electric telegraph；' as Sir William Thomson happily expressed it； was followed by another invention in some respects even more remarkable。 During the winter of 1878 Professor Bell was in England； and while lecturing at the Royal Institution； London； he conceived the idea of the photophone。 It was known that crystalline selenium is a substance peculiarly sensitive to light； for when a ray strikes it an electric current passes far more easily through it than if it were kept in the dark。 It therefore occurred to Professor Bell that if a telephone were connected in circuit with the current； and the ray of light falling on the selenium was eclipsed by means of the vibrations of sound； the current would undulate in keeping with the light； and the telephone would emit a corresponding note。 In this way it might be literally possible 'to hear a shadow fall athwart the stillness。'
He was not the first to entertain the idea； for in the summer of 1878； one 'L。 F。 W。；' writing from Kew on June 3 to the scientific journal NATURE describes an arrangement of the kind。 To Professor Bell； in conjunction with Mr。 Summer Tainter； belongs the honour of having； by dint of patient thought and labour； brought the photophone into material existence。 By constructing sensitive selenium cells through which the current passed； then directing a powerful beam of light upon them； and occulting it by a rotary screen； he was able to vary the strength of the current in such a manner as to elicit musical tones from the telephone in circuit with the cells。 Moreover； by reflecting the beam from a mirror upon the cells； and vibrating the mirror by the action of the voice； he was able to reproduce the spoken words in the telephone。 In both cases the only connecting line between the transmitting screen or mirror and the receiving cells and telephone was the ray of light。 With this apparatus； which reminds us of the invocation to Apollo in the MARTYR OF ANTIOCH
'Lord of the speaking lyre； That with a touch of fire Strik'st music which delays the charmed spheres。'
Professor Bell has accomplished the curious feat of speaking along a beam of sunshine 830 feet long。 The apparatus consisted of a transmitter with a mouthpiece； conveying the sound of the voice to a silvered diaphragm or mirror； which reflected the vibratory beam through a lens towards the selenium receiver； which was simply a parabolic reflector； in the focus of which was placed the selenium cells connected in circuit with a battery and a pair of telephones； one for each ear。 The transmitter was placed in the top of the Franklin schoolhouse； at Washington； and the receiver in the window of Professor Bell's laboratory in L Street。 'It was impossible；' says the inventor； 'to converse by word of mouth across that distance； and while I was observing Mr。 Tainter； on the top of the schoolhouse； almost blinded by the light which was coming in at the window of my laboratory； and vainly trying to understand the gestures he was making to me at that great distance； the thought occurred to me to listen to the telephones connected with the selenium receiver。 Mr。 Tainter saw me disappear from the window； and at once spoke to the transmitter。 I heard him distinctly say； 〃Mr。 Bell； if you hear what I say； come to the window and wave your hat！ 〃 It is needless to say with what gusto I obeyed。'
The spectroscope has demonstrated the truth of the poet； who said that 'light is the voice of the stars；' and we have it on the authority of Professor Bell and M。 Janssen； the celebrated astronomer； that the changing brightness of the photosphere； as produced by solar hurricanes； has produced a feeble echo in the photophone。
Pursuing these researches； Professor Bell discovered that not only the selenium cell； but simple discs of wood； glass； metal； ivory； india… rubber； and so on； yielded a distinct note when the intermittent ray of light fell upon them。 Crystals of sulphate of copper； chips of pine； and even tobacco…smoke； in a test…tube held before the beam； emitted a musical tone。 With a thin disc of vulcanite as receiver； the dark heat rays which pass through an opaque screen were found to yield a note。 Even the outer ear is itself a receiver； for when the intermittent beam is focussed in the cavity a faint musical tone is heard。
Another research of Professor Bell was that in which he undertook to localise the assassin's bullet in the body of the lamented President Garfield。 In 1879 Professor Hughes brought out his beautiful induction balance； and the following year Professor Bell； who had already worked in the same field； consulted him by telegraph as to the best mode of applying the balance to determining the place of the bullet； which had hitherto escaped the probes of the President's physicians。 Professor Hughes advised him by telegraph； and with this and other assistance an apparatus was devised which indicated the locality of the ball。 A full account of his experiments was given in a paper read before the American Association for the Advancement of Science in August； 1882。
Professor Bell continues to reside in the United States； of which he is a naturalised citi
