MECHANICS AND USEFUL ARTS. 53 



AMERICAN COMPOUND TELEGRAPH WIRE. 



There is a growing tendency in this and other countries to era- 

 ploy larger wire for telegraph purposes, in order to obtain a 

 greater conducting capacity. 



Notwithstanding the many disadvantages attending the use of 

 large telegraph wire, No. 4 has been adopted on important lines 

 and for long circuits, in England, Russia, and other countries, 

 solely for its superior conductivity; audit is well understood by 

 telegraphers in general, that, for the rapid and successful opera- 

 tions of the circuits, much depends upon this element. Especially 

 is this the case in wet weather and upon long lines. 



Under certain conditions of the lines, consequent upon wet 

 weather, superior conductivity will accomplish that which increased 

 battery power utterly fails to do ; and repeaters at intermediate 

 oflBces, with their necessary main batteries, accomplish but im- 

 perfectly and unsatisfiictorily, as a general rule, and in many cases 

 fail altogether. 



Pure copper wire, having a conducting capacity of nearly 7 

 times that of galvanized iron wire, has a great advantage in this 

 respect for telegraph purposes. Its use, however, has been pre- 

 vented in consequence of lack of sufficient strength to sustain 

 itself. 



In the American Compound Telegraph Wire this vital objection 

 to the employment of copper alone for this purpose is obviated, 

 and a conductivity and relative strength, superior to that of gal- 

 vanized iron, are combined in a lighter wire. 



The composite parts of this wire are steel and copper, the steel 

 forming the core, and serving mainly for strength, while the 

 copper serves more especially as a superior conductor. 



In regard to relative strength, it is well known that the breaks 

 in ordinary galvanized telegraph wire, occasioned by accumula- 

 tions of ice and snow, and from other causes, occur at weak 

 points, or at imperfections which are caused b}' flaws existing in 

 the iron before galvanizing, as well as from the effects of that 

 process. 



It is therefore claimed that the compound wire, even with a rel- 

 ative strength no greater, theoreticall}', than that of a galvanized 

 iron wire, will be much less liable to breakage from these causes, 

 in consequence of the uniformity of strength in the steel core, 

 while, in fact, the relative strength itself of the compound wire 

 is very much the better of the two. 



Steel wires, of sizes varying from No. 12 to No. 16, stretched 

 from pole to pole, across streams from one-quarter to three-quar- 

 ters of a mile in width, in the United Slates, which have with- 

 stood the accumulations of ice and sleet for years, are good illus- 

 trations in this connection. One special instance may be cited, of 

 a No. 16 steel wire, between 1,400 and 1,500 feet in length, which 

 has been in operation across the Kennebec River, in Maine, for the 

 past 8 years, and which has parted twice only during that period, 

 — in each case having been untwisted at a joint by the great 



