That the tone is made audible at a distance by the electric agitations, and not by direct conduction of the sound-waves through the wires is proved in the most evident way of all, because one instantly hears no more the tone through the spiral when a good short circuit is made, as, for example, by laying upon the two wires which conduct the electricity a strip of sheet metal right in front of the spiral.
The reproduced tones are, of course, somewhat weaker than the original ones, but the number of vibrations is similar. If thus the reproduction [of tones] in exactly similar height and depth is easily attained, it is however difficult for our ear, amidst the always smaller vibrations, to which the diminished strength of the tone is due, to evaluate exactly the magnitude of the vibrations. But the character of the tone depends upon the number of variations of amplitude (Anschwellungen), that is to say, depends upon whether, for example, in the tones which have similar pitch and therefore a similar number of waves per second, the fourth, sixth, eighth, tenth, or sixteenth wave is stronger than the others. For physicists have shown that an elastic spring is set in vibration by the thrust of the teeth of a cog-wheel; the first vibration is the greatest, all those that follow being less. If there comes, before the spring comes to rest, a fresh thrust from a cog, then the next vibration is again equal to the greatest first vibration without the spring making any more vibrations on that account; and by this means vowel-tones may be artificially produced.
One may also be yet far removed from being able to carry on a conversation with a friend dwelling a hundred miles distant, and recognise his voice, as if he sat near us; but it can no longer be maintained that this is impossible. Indeed the probability that this will be attained[23] is already become as great as the probability of the reproduction of natural colours in photography has become through the notable researches of Niepce.
[The second public exhibition which Reis made of the telephone was, like the first, in Frankfort-on-the-Main, but this time before a Society known as the _Freies Deutsches Hochstift_, or Free German Institute, a kind of Athenæum Club for the city of Frankfort, now for many years established in the well-known house where the poet Goethe was born, in the Grosse Hirschgraben. In 1862, however, the Free German Institute held its meetings in another building known as the Saalbau. And on May the 11th of that year Philipp Reis lectured upon and exhibited the Telephone. A journal which appeared then, and still appears, in Frankfort, with the title of ‘Didaskalia,’ devoted to light literary and artistic news, popular science, and general intelligence of an informing character, ordinarily inserted notices of the chief meetings of the Hochstift. On this occasion a preliminary paragraph was inserted in the following terms:--]