140 METHODS OF COMMUNICATION FOR FOREST PROTECTION 



easily be iseveral times as great as the resistance of the coils, and the bulk of the cur- 

 rent would, therefore, be shunted. to the ground through the bells of the nearest instru- 

 ments and would not reach the more distant instruments in sufficient amount' to ring- 

 them. Bridging bells, therefore, are wound with coils of very high resistance 

 2,500 ohms in the Forestry Branch instruments only by this means the ringing cur- 

 rent is made to traverse the entire line and only enough passes to the ground through 

 each bell to ring it properly. These high-resistance bell coils also effectively bar out 

 escape of the talking current. Although this is not so much the result of their resis- 

 tance as it is of the impedance resulting from the peculiar construction of these coils, 

 it is thoroughly effective in confining the talking current to the line and preventing 

 leakage to the ground through the bells which are, as stated, continuously in circuit on 

 all instruments. The importance, however, of having all coils of the same resistance 

 will be evident, since the introduction of a low-resistance 'bell will divert to the ground 

 an excess amount of current to the detriment of all other instruments on the line. 



CHAPTER XV 



OPERATION 



Section 88 Operating Rules 



On every telephone system there should be a definite set of rules to govern the 

 operation of the lines and stations. These are usually very simple and should be 

 made up in the form of a printed or typewritten card and fastened to the wall close 

 beside the instrument, or directly over it on the post or tree support in case of out- 

 door stations. This card should also contain a complete list of all stations and call 

 signals on the line and directions for getting connections through central switching 1 

 stations to other lines if necessary. All such switching stations should be mentioned 

 with the points to which connections may be had through them. In many cases, 

 instruments are used by persons not connected with the fire-protection staff to send 

 news of fires or other messages during the absence of the ranger, or from a field 1 

 station. Operating rules should be framed to en-able such persons to use the telephone 

 Hine without difficulty or delay. 



In all cases rules for operation should provide against persons " ringing in " on the 

 line when it is in use and for " ringing off " when through using the line. Two rules 

 to cover these provisions are: 



1 Before ringing any station, " listen in " on the line and inquire if the line is 

 busy. Do not ring while the line is in use by others. 



2 On finishing a conversation, both stations must ring off by giving one short ring. 



Section 89 Code Signalling 



1 METHOD EMPLOYED 



The calls of various stations are made by long and short rings variously arranged. 

 As a rule not more than four such rings need to be included in any one call or signal. 

 Those stations which are called most often should have the most simple signals and 

 those called least often, the most intricate. It must be noted, however, that " longs ;r 

 transmit somewhat better than "shorts" over lines that are in poor condition, so that 

 -distant stations should, as a rule, have signals largely made up of long rings while the 



