pitch, strength and quality unchanged; the comprehensive scope of the newly-created art of speech transmission; the remarkable transmitting qualities of the first of all electric-speaking telephones; and the promptness with which the inventor placed before the public a full and complete knowledge of his invention and of the essential steps leading to his application for letters-patent, all go to prove the possession in. 1874—6 of an unusual knowledge on the part of Alexander Graham Bell, the more remarkable in view of the slight grasp electricians then possessed of magnetic action and the interrelation of the magnetic field and the electric current.
II. The Telephone Exhibit at the Centennial Exposition
In 1874, Alexander Graham Bell evolved his magnificent conception of the transmission of speech over long distances by means of the electric-speaking telephone. Theoretically it was perfect; practically it had no tangible existence. Men eminent in their respective professions, to whom he confided his plans in the autumn of 1874, admitted that while in theory the undulating-current method 'was adequate to the transmission of speech,' yet the electrical effect produced by the vibration of a diaphragm-armature actuated only by the human voice 'would be entirely too small to accomplish the desired end.' In fact, so complete was the absence of practical knowledge concerning the electrical effect that would be produced by causing the spoken word to vibrate an armature in front of an electro-magnet that the experts, most competent to pass upon the value of such an invention as the electric-speaking telephone, testified that the state of the art was such at the date of the patent that it could hardly have been supposed that a magneto-generator moved by a force so slight as the spoken word, 'would under any circumstances be able to generate an electric current which would produce upon a receiving instrument any effect whatever which would be perceptible to the senses.'
Discouraging though the advice and the suggestions of his friends proved, and disheartened though he was by ill-health and the lack of funds to carry on his telephone experiments, never did the inventor allow aught to divert his firm purpose of transforming that marvelous theory into a tangible speech-transmitting telephone.
In 1874, Alexander Graham Bell occupied the chair of vocal physiology in the Boston University, and supplemented his lectures 'by experimental demonstration of the practicability of correcting stammering, stuttering, lisping, burring and other defects of speech.' To a class composed exclusively of teachers of the deaf who had been sent to Boston by various institutions for the deaf throughout the United States, he delivered courses of lectures upon the subject of teaching articulation to deaf pupils, experimentally demonstrating his methods by giving instruction to deaf-mutes. He also had a class of
