Page:Popular Science Monthly Volume 12.djvu/582

The longest distance at which conversation has been carried on, so far, through the telephone, is about 250 miles. With a submarine Fig. 7. cable conversation has been carried on between England and France across the English Channel. Conversation has also been held through the bodies of sixteen persons standing hand-in-hand. The telephone has been regarded as a toy, or a curiosity to be played with; but, while it is undoubtedly extremely interesting as a novelty, it is very much more than this; it is, scientifically and practically, a great success. There are, undoubtedly, difficulties in its use, but, considering that it is a contrivance but of yesterday, the wonder is that it is so perfect. The telegraph was much longer regarded as an impracticable invention, and it is impossible to say how soon the telephone may not take rank among the necessities of common life. If we may trust the analogies of experience, its difficulties are certain to be overcome, although it will probably never meet the exaggerated expectations of many people. Some of the obstacles to the realization of the popular impression of its capabilities have been so well stated in Chambers's Journal, by a gentleman skilled in the working of the telegraph, and who made a series of interesting experiments *on the telephone, that we may fitly close our article by making free extracts from his paper, accompanied by some slight revision: When a telegraphist first gets into his hand this beautifully simple and electrically delicate instrument, his first inclination is to test its carrying-power. This is, of course, a closet experiment, not working with actual telegraph-line, but with 'resistance' equivalent to a telegraph-line of stated length. An experiment of this nature gives better results than could be obtained by a veritable line, because the insulation is, so to speak, perfect. No leakage at undesigned points of contact, or disturbance from unfavorable atmospheric conditions, is felt, and the experiment is entirely under the observer's control. The apparatus used is designed to offer the same labor for the electric current to overcome as would be offered by a stated length of outside telegraph-line. This artificial resistance is nicely graduated, and, as the method of testing was suggested by Ohm, a German electrician, the unit of resistance is termed an 'ohm.' Removing the telephone to such a distance that the two observers were 'out of ear-shot,' the test with resistance was tried, and with a resistance of 1,000 ohms—roughly speaking, equal to seventy miles of a well-constructed line—the sound was perfect, although not very loud. Every articulation of