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THE POPULAR SCIENCE MONTHLY. 



Fig. 7. 



The longest distance at which conversation has been carried on, 

 so far, through the telephone, is about 250 miles. With a submarine 



cable conversation has been carried on between 

 England and France across the English Chan- 

 nel. 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 nov- 

 elty, it is very much more than this ; it is, sci- 

 entifically 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 ex- 

 aggerated 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 ex- 

 periments *on the telephone, that we may fitly close our article by mak- 

 ing 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 tele- 

 graph-line of stated length. An experiment of this nature gives bet- 

 ter 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 cur- 

 rent 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 



