28 Transactions of the Kansas 



th<iugli if too small or too thin the tones had a nasal character, while it sounded 

 like talking into a barrel if the plates were too thick or too broad. Likewise in the 

 battery, he left off one cell after another, until finally all were removed, and still 

 he could talk through the instrument. This was due to residual magnetism as he 

 afterward found, but it led to the abandonment of batteries and the substitution 

 of permanent magnets tor the iron cores. This is the form in which the Bell tele- 

 phone is now used, with no battery and no continuous current, being purely mag- 

 neto-electric in its principle of action. It must be evident, prima facie, that such 

 a telephone can only talk in low tones. Only a small part of the original sound 

 impulse can be changed into electricity, and this in turn can deliver but a small 

 fraction of its force to the ear of the listener. It has been, therefore, from the 

 first, a desideratum to increase the loudness of telephone messages. In quality 

 they were all that could be desired, but the still small voice was hard to be distin- 

 guished by unpracticed ears. Hence the long continued experiments of Prof. Bell 

 alluded to. It was found that if an increase was attempted by shouting the origi- 

 nal message, the quality of that delivered was much impaired. The sounds, though 

 louder, became indistinct and unintelligible. This was owing to another principle 

 of electro-magnetism, which came into operation in such a case. The electric 

 intensity of telephonic currents depends not only on motion of magnet being 

 directly proportional to velocity of the vibrating plate, but they are inversely as 

 square of distance. Now when the motion of the plate is very small, perhaps 

 chiefly molecular, when moderate tones are used, the variation of distance is so 

 small as to give no appreciable difference on this account ; but when the tones are 

 loud, the air-waves give the plate such motion that the law of inverse squares comes 

 in, and the electric pulsation is no longer a faithful copy of the sound-wave. 



All attempts, then, to increase loudness by larger battery power, varying the 

 dimensions of the plate, or by increasing the volume of tone at the transmitting 

 station, fail, in great degree, to reach the end sought. Many inventors have tried 

 their skill at this problem without much success. The question then arises, is there 

 not some other way, save by motion of a magnet, of modifying the electric current 

 so that it shall faithfully represent sound-waves? 



This leads us to the third class of electric telephones, of which Mr. Edison's 

 inventions furnish the best examples. The genius of Menlo Park, whose fame is 

 word-wide now, owes his reputation most of all to the phonograph, an invention 

 suggested, doubtless, by Bell's telephone, in an attempt to improve the hitler. It 

 is not my purpose to discuss this at all, though it is not a little curious that Edison, 

 seeking to improve on Bell's discovery, should incidentally solve Bell's original 

 problem, and, not only that, should also hit on a new line of telephone improve- 

 ment which vastly increases the possibilities of this invention. All workers with 

 current electricity know how important it is to secure firm metallic contacts in 

 conductors. Here is an invention whose success depends on a loose contact. 

 Edison's merit and success in telephones probably lies chiefly in the invention of 

 the carbon button, which, likewise, is the foundation of the tasimeter and a 

 dozen other novel instruments. It, therefore, merits a special description, easy to 

 give, for it consists simply of compressed lamp-black arising from incomplete 

 combustion of coal oil. It is pressed, with a force of 1,000 pounds to the square 

 inch, into the form of a little disc, one-half of an inch in diameter, and one-sixteenth 

 of an inch thick, the breadth and thickness of an old-fashioned wafer for sealing 

 letters. The carbon button is placed between two metallic discs, which are, in turn, 

 joined to wires forming opposite poles of an electric circuit. The electric current, 

 therefore, passes through the carbon. Tiie discs which form the sides of the 



