Page:Popular Science Monthly Volume 9.djvu/97

Rh least confusion ensued from the crowding together, for a considerable distance, of the multitude of intricately-related vibrations in a rod having a section of but one square inch.

Prof. Helmholtz's apparatus consisted of a number of electro-magnets acting on tuning-forks pitched to particular notes. His object was so to combine those notes as to demonstrate the formation of certain harmonious sounds; but the object of the telegraph-inventors is the reverse of that, namely, to transmit them in the form of electric vibrations to a distance, and then—as in Wheatstone's experiment—to sift them out again to separate instruments. In most of the plans so far made public, a fixed steel bar takes the place of the tuning-fork, and therefore of the armature as well. When attracted by the magnet, on making a signal, it is of course set vibrating; and, at every forward vibratory movement, it closes the circuit and transmits an electric impulse. A number of such magnets, their sonorous armatures sending each a different number of pulsations in a second, may be working away at once, and the corresponding instruments at the other end of the line will be acted on only by those which suit their times of vibration. In other words, of the total number of electric charges sent into the line, only those will act on any particular magnet at the receiving end which suffice to cause in its armature the number of vibrations per second to which it was set. This, of course, is the same number which was sent by the transmitting instrument of the same pair. Practically, the different tones are not reproduced quite unmixed, every armature being capable of responding though in a less degree, to other notes than its own; so that the effect on the ear, at one of the receiving magnets, is like that of a number of persons talking together in different keys: some quite loudly; some in a lower tone; others in a whisper. To remedy this, different forms of resonators are being tried, adapted to swell the special sounds that should be heard.

The "electromotograph," described in connection with chemical telegraphs, is intended, by its inventor, to be used with some form of this acoustic system. Mr. Gray, of Chicago, another well-known telegraph-inventor, is also understood to have made considerable progress in this direction.

It is matter of reasonable pride to find, at the commencement of our second century, the names of Americans so prominently connected with all the great improvements in the art which owes so much to the labors of Morse and Henry.