32 METHODS OF COMMUNICATION FOR FOREST PROTECTION 



poplar is old and defective, windfall is light and the width of clearing need not be 

 excessive 20 to 25 ft. in stands of sound green timber not over 40 to 50 ft. high being 

 adequate. Care should be taken to cut all snags or defective trees, outside this right 

 of way, that threaten to fall on the line. 



3 DEAD TIMBER 



There remains then only the question of dead standing timber. This is the most 

 troublesome kind of .stand through which to build and maintain a telephone line. 

 Whenever possible, such timber should be carefully avoided, even at the expense of a 

 material lengthening of the line. The foregoing applies not only to forests in which 

 all the trees are dead but also to forests in which a considerable proportion of the trees 

 are dead or badly decayed and where windfalls are consequently frequent and such 

 forests are extremely undesirable along the line. Where, as sometimes happens, it is 

 entirely impossible to avoid constructing through such stands and an adequate right 

 of way cannot be cleared, then the most careful attention must be given to the details 

 of tree-line construction and the line must Toe constantly maintained in first-class con- 

 dition. This latter is of extreme importance because the accumulation of several 

 fallen snags across the line in a short distance will take up all the slack and cause the 

 intervening portions to be drawn up very tightly. If this tight wire should happen to 

 be caught on a projecting branch, or even if the ties fail to break as quickly as 

 designed, then any new windfalls coming on the line will very likely cause a break. 

 Even if no break occurs the line is sure to be very seriously strained and a large 

 number of ties pulled off or broken, insulators smashed, and general havoc created. 

 Only by careful and conscientious maintenance may lines be kept operating through 

 large dead standing timber where windfall is frequent. 



Section 38 Grounded versus Metallic Circuits 



A grounded circuit is one in which only a single wire is employed for the trans- 

 mission of the calling and talking currents and the earth is utilized as the other half, 

 or return portion, of the circuit. 



A metallic circuit employs two wires, the extra wire taking the place of the earth 

 or return portion of the circuit in a grounded line. 



Contrary to what appears to be popular opinion it is not necessarily possible to 

 talk farther over a metallic than over a grounded! circuit. On the contrary, since the 

 earth for all practical purposes may be assumed to interpose no resistance to the 

 return currents, provided the ground connections are well made and do not themselves 

 offer a higher resistance, a grounded circuit will have only one-half the electrical resist- 

 ance of a metallic circuit under similar conditions. From this it does not necessarily 

 follow that it is possible to talk twice as far over a grounded circuit, because conditions 

 other than the mere electrical resistance of the intervening wire have an important 

 influence on the possibilities of long distance telephonic transmission. The usefulness 

 of metallic circuits arises from the possibilities of eliminating from them, by suitable 

 transpositions, all induced currents from other electrical circuits such as power, light, 

 telegraph, or telephone lines that may exist in their vicinity. The extraneous noises 

 or cross-talk on a grounded circuit of even short length which runs close to such cur- 

 rents often make distinct speech transmission impossible, regardless of the electrical 

 resistance of the line itself. By using a two-wire, or metallic, circuit such interference 

 from outside sources may be eliminated by transposition, and communication is thus 

 rendered possible where a one-wire, or grounded, line cannot be used at all. Where, 

 however, difficulties in transmission arise, not from interference by induced currents 

 but from excessive length of lines, poor insulation, bad joints, poor " grounds," or 

 other defects in construction, the installation of a metallic circuit will give no relief. 

 Excessive line length can only be remedied by using a more efficient conductor. Thus, 



