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1868。 In this he explains his ingenious method of instructing deaf mutes； by means of their eyesight； how to articulate words； and also how to read what other persons are saying by the motions of their lips。 Graham Bell； his distinguished son； was educated at the high school of Edinburgh； and subsequently at Warzburg； in Germany； where he obtained the degree of Ph。D。 （Doctor of Philosophy）。 While still in Scotland he is said to have turned his attention to the science of acoustics； with a view to ameliorate the deafness of his mother。
In 1873 he accompanied his father to Montreal； in Canada； where he was employed in teaching the system of visible speech。 The elder Bell was invited to introduce it into a large day…school for mutes at Boston； but he declined the post in favour of his son； who soon became famous in the United States for his success in this important work。 He published more than one treatise on the subject at Washington； and it is； we believe； mainly through his efforts that thousands of deaf mutes in America are now able to speak almost； if not quite； as well as those who are able to hear。
Before he left Scotland Mr。 Graham Bell had turned his attention to telephony； and in Canada he designed a piano which could transmit its music to a distance by means of electricity。 At Boston he continued his researches in the same field； and endeavoured to produce a telephone which would not only send musical notes； but articulate speech。
If it be interesting to trace the evolution of an animal from its rudimentary germ through the lower phases to the perfect organism； it is almost as interesting to follow an invention from the original model through the faultier types to the finished apparatus。
In 1860 Philipp Reis； as we have seen； produced a telephone which could transmit musical notes； and even a lisping word or two； and some ten years later Mr。 Cromwell Fleetwood Varley； F。R。S。； a well…known English electrician； patented a number of ingenious devices for applying the musical telephone to transmit messages by dividing the notes into short or long signals； after the Morse code； which could be interpreted by the ear or by the eye in causing them to mark a moving paper。 These inventions were not put in practice； but four years afterwards Herr Paul la Cour； a Danish inventor； experimented with a similar appliance on a line of telegraph between Copenhagen and Fredericia in Jutland。 In this a vibrating tuning…fork interrupted the current； which； after traversing the line； passed through an electro…magnet； and attracted the limbs of another fork； making it strike a note like the transmitting fork。 By breaking up the note at the sending station with a signalling key； the message was heard as a series of long and short hums。 Moreover； the hums were made to record themselves on paper by turning the electro…magnetic receiver into a relay； which actuated a Morse printer by means of a local battery。
Mr。 Elisha Gray； of Chicago； also devised a tone telegraph of this kind about the same time as Herr La Cour。 In this apparatus a vibrating steel tongue interrupted the current； which at the other end of the line passed through the electro…magnet and vibrated a band or tongue of iron near its poles。 Gray's 'harmonic telegraph；' with the vibrating tongues or reeds； was afterwards introduced on the lines of the Western Union Telegraph Company in America。 As more than one set of vibrationsthat is to say； more than one notecan be sent over the same wire simultaneously； it is utilised as a 'multiplex' or many…ply telegraph； conveying several messages through the same wire at once； and these can either be interpreted by the sound； or the marks drawn on a ribbon of travelling paper by a Morse recorder。
Gray also invented a 'physiological receiver；' which has a curious history。 Early in 1874 his nephew was playing with a small induction coil； and； having connected one end of the secondary circuit to the zinc lining of a bath； which was dry； he was holding the other end in his left hand。 While he rubbed the zinc with his right hand Gray noticed that a sound proceeded from it； which had the pitch and quality of the note emitted by the vibrating contact or electrotome of the coil。 'I immediately took the electrode in my hand；' he writes； 'and； repeating the operation； found to my astonishment that by rubbing hard and rapidly I could make a much louder sound than the electrotome。 I then changed the pitch of the vibration； and found that the pitch of the sound under my hand was also changed； agreeing with that of the vibration。' Gray lost no time in applying this chance discovery by designing the physiological receiver； which consists of a sounding…box having a zinc face and mounted on an axle； so that it can be revolved by a handle。 One wire of the circuit is connected to the revolving zinc； and the other wire is connected to the finger which rubs on the zinc。 The sounds are quite distinct； and would seem to be produced by a microphonic action between the skin and the metal。
All these apparatus follow in the track of Reis and Bourseulthat is to say； the interruption of the current by a vibrating contact。 It was fortunate for Bell that in working with his musical telephone an accident drove him into a new path； which ultimately brought him to the invention of a speaking telephone。 He began his researches in 1874 with a musical telephone； in which he employed the interrupted current to vibrate the receiver； which consisted of an electro…magnet causing an iron reed or tongue to vibrate； but； while trying it one day with his assistant； Mr。 Thomas A。 Watson； it was found that a reed failed to respond to the intermittent current。 Mr。 Bell desired his assistant； who was at the other end of the line； to pluck the reed； thinking it had stuck to the pole of the magnet。 Mr。 Watson complied； and to his astonishment Bell observed that the corresponding reed at his end of the line thereupon began to vibrate and emit the same note； although there was no interrupted current to make it。 A few experiments soon showed that his reed had been set in vibration by the magneto…electric currents induced in the line by the mere motion of the distant reed in the neighbourhood of its magnet。 This discovery led him to discard the battery current altogether and rely upon the magneto…induction currents of the reeds themselves。 Moreover； it occurred to him that； since the circuit was never broken； all the complex vibrations of speech might be converted into sympathetic currents； which in turn would reproduce the speech at a distance。
Reis had seen that an undulatory current was needed to transmit sounds in perfection； especially vocal sounds； but his mode of producing the undulations was defective from a mechanical and electrical point of view。 By forming 'waves' of magnetic disturbance near a coil of wire； Professor Bell could generate corresponding waves of electricity in the line so delicate and continuous that all the modulations of sound could be reproduced at a distance。
As Professor of Vocal Physiology in the University of Boston； he was engaged in training teachers in the art of instructing deaf mutes how to speak； and experi