Page:Heroes of the telegraph (IA cu31924031222494).djvu/240

 he knew that a metal tympanum was capable of vibrating with all the delicacies of speech, and it occurred to him that if these vibrations could be impressed on a yielding material, as the Morse signals were embossed upon the paper, the indentations would reproduce the speech, just as the furrows of the paper reproduced the Morse signals. The tympanum vibrating in the curves of speech was instantly united in his imagination with the embossing stylus and the long and short indentations on the Morse paper; the idea of the phonograph flashed upon him. Many a one versed in acoustics would probably have been restrained by the practical difficulty of impressing the vibrations on a yielding material, and making them react upon the reproducing tympanum. But Edison, with that daring mastery over matter which is a characteristic of his mechanical genius, put it confidently to the test.

Soon after this experiment, a phonograph was constructed, in which a sheet of tinfoil was wrapped round a revolving barrel having a spiral groove cut in its surface to allow the point of the indenting stylus to sink into the yielding foil as it was thrust up and down by the vibrating tympanum. This apparatus—the first phonograph—was published to the world in 1878, and created a universal sensation. It is now in the South Kensington Museum, to which it was presented by the inventor.

The phonograph was first publicly exhibited in England at a meeting of the Society of Telegraph Engineers, where its performances filled the audience with astonishment and delight. A greeting from Edison to his electrical brethren across the Atlantic had been impressed on the tinfoil, and was spoken by