THE MAGNETO TELEPHONE 117 



best to let the grounding facilities determine the place of connection if possible. The 

 best place is the margin of a stream, pond, or slough, where the ground rod may be 

 set in the wet soil or mud. Do not try to ground in water alone, or in a Tocky bottom. 

 If a natural wet place is not convenient, ground in loose, moist soil and after setting 

 the ground rod pour a pail of water over it 



The special portable ground rod, Northern Electric No. 313-B, usually known 

 as the bayonet ground rod (Fig. 62), is useful with emergency kits, but for use by 

 patrolmen with portable telephones it should be replaced by a large hunting-knife. 

 The bayonet rod is a singularly useless instrument except for its one special purpose, 

 and when weight is an important consideration, as with patrolmen or " smoke 

 chasers," the hunting-knife is preferable. A fairly large blade is necessary in order 

 to make a good ground. At the base of the blade close up against the handle a brass 

 binding-post should be inserted and soldered to the blade. The Cree knife shown 

 in Figs. 64 and 66 has a blade 9 in. long by 2 in. wide and serves admirably for 

 grounding a portable telephone, but a smaller knife may be used. Very good ground 

 rods -can be made of heavy jointed brass rifle cleaning rods, and these may be car- 

 ried in tne case of either of the portable telephones. It is probable that the need for 

 a satisfactory portable ground will result in development in this direction. 



CHAPTER XIV 



MAGNETO TELEPHONE 



Section 84 Introduction 



It is a matter of common knowledge that the purpose of the telephone is to 

 enable conversation to be carried on between two persons who are beyond ordinary 

 talking distance from each other, and that this is accomplished by converting the 

 air vibrations of the voice into electrical vibrations which are carried to the distant 

 person over a wire or electrical conductor and there converted into air vibrations or 

 sounds of the same character. The modern commercial instruments have been 

 brought to such a high state of perfection and are so nearly " foolproof " that it is 

 possible for persons entirely without knowledge of the principles on which these 

 instruments operate to install and use them with entire success by observing a few 

 simplo precautions, following directions, and using plain common sense. It is very 

 desirable, however, that those who have charge of extended telephone systems, such 

 as are now commonly used in specialized forest protection, should have some under- 

 standing of the fundamentals of the telephone. Unfortunately, to understand the 

 operation of this instrument requires some knowledge of practically every branch 

 of electrical science, because nearly every branch is to some extent utilized in the 

 modern telephone. For the benefit of those desiring a full understanding of this 

 instrument a comprehensive list of books of reference has been inserted in Appen- 

 dix B. 



The description of the telephone instrument contained in 'this manual is intended 

 for those who have little or no knowledge of the science of telephony, and should 

 be regarded only as an introduction to this science. 



It is necessary, however, to assume the possession of a knowledge of the funda- 

 mental electrical phenomena. Those unacquainted with even the elementary facts of 

 electrical science will first have to consult some standard text booK oil the subject. 

 Certain definitions, however, of technical terms most frequently employed in the 

 s-cience of telephony may assist in an understanding of the text, and are therefore 

 included in this manual. 



