and vulcanized rubber, is pressed by means of a long 

 spring, the amount of pressure being adjusted by a 

 screw near the base. This transmitter worked admir- 

 ably, and, as improved by the inventor shortly after, con- 

 stituted an excellent and practical instrument. Other 

 transmitters were invented by Professor Hughes and 

 Francis Blake, the Hughes transmitter being the 

 popular one in Europe, while the Blake transmitter 

 came generally into use in America. 



Within the last few years what is known as the long- 

 distance telephone, connecting points at a distance of 

 a thousand miles or more, has been perfected. This 

 does not differ in principle, of course, from the ordi- 

 nary telephone, the difference being represented largely 

 by the material used in the conducting wires. For 

 short distances the ordinary iron wire answers all 

 practical requirements; but this material is a rela- 

 tively poor conducting medium, and copper, being a 

 much better conductor, is necessary for long-distance 

 telephones. 



In addition to this improvement in the conducting 

 medium it has been found necessary to increase the sen- 

 sitiveness of the transmitter in long-distance telephones. 

 For, unlike the telegraph, no practical system of relays 

 for strengthening the current has been perfected as yet, 

 although the limit of long-distance telephony is greatly 

 increased by inserting self-induction coils at intervals 

 along the line. 



The first long-distance transmitter was what is 

 known as the Runnings' transmitter. This consists 

 of a shallow vertical box with insulated sides, and 



[84] 



