THE MAGNETO TELEPHONE 



133 



This was accomplished in the 100-i-A hand set by using for signalling a n induced 

 current of high potential and high frequency acting upon a special typs of telephone 

 receiver at the distant station. The wonderful sensitiveness of the receiver to small 

 currents of this kind has previously been explained. By this system, therefore, it is 

 possible to work over very faulty lines where the ordinary generator currents are 

 entirely lost through leakage or high resistance. The howler is the special form of 

 receiver used to receive vibratory signals. It is the same aa the ordinary receiver 

 already described except that the pole pieces of the long, horseshoe magnet are 

 "attached to it at right angles. This is mounted in a wooden block for convenient 

 attachment to the wall and is prov : dei with a small megaphone which serves to con- 

 centrate the sound waves given off by the vibrating diaphragm. Howlers are con- 

 nected between the telephone and the protector so that they are protected from injury 

 by lightning or other high-tension currents and v are not likely to get out of order. 

 They must be carefully adjusted so as to produce the maximum sound, the adjust- 

 ment being accomplished by tightening or loosening the screw-cap which holds the 

 diaphragm in place. The type of howler used by the Forestry Branch is shown in 

 Fig. 82. 



(c) LigJi-tning-arrester. It is always necessary to protect telephone instruments 

 against lightning. This is particularly true on many long-d'istance forest lines which 

 cross through regions of high altitude where lightning is sometimes very prevalent. 

 It is also necessary to provide special protection wherever telephone lines are liable 



Fig. 83 Lightning protector for use where there are no power 

 or light wires 



to come iii contact with wires bearing electric-light or power currents. Two types 

 of protective devices are employed. In the lightning-arrester used by the Forestry 

 Branch advantage is taken of the fact that a high-tension current such as lightning 

 will jump a small air gap in seeking the shortest path to the ground rather than pass 



