Sunday, July 24, 2005

Telegraph Line to Promontory


I'm trying to work out a calculation of the voltage required to work the telegraph wire from Promontory to Sacramento.   

If the wire were copper, and if the only stations having telegraph instruments "cut into" the wire were Sacramento and Promontory, the number comes out to around 200 volts!  That's a lot of power when you're using "primary cells" (zinc, copper and battery acid) giving an output of around 1.5 volts per cell.  The more stations having instruments cut in, the higher the required voltage becomes.  

So I need to answer some questions.  Does anyone have information on the following topics?  

(1)  Did the Central Pacific use copper wire in the construction of its telegraph line, or the much cheaper iron wire?  

(2)  Did the poles at Promontory in 1869 carry one telegraph wire, or two?  Can anyone tell from the photographs?  (The 1877 Report to the House of Representatives indicates two insulators per cross arm, which would seem to indicate two wires.)  If there are two wires showing on those poles at Promontory, it is a reasonable assumption that one was for "local" traffic between the way stations, and one was a "through" wire back to Sacramento.  

(3)  Did the telegraphers at Promontory work "directly" with Sacramento on a "through" wire, or did their messages have to be "relayed" (copied and re-transmitted) by one or more offices midway along the line?  

Oh, I should explain one thing ... A Morse telegraph circuit (unlike a telephone circuit) needs only ONE wire to function.  An iron stake is driven into the ground at both ends of the telegraph wire, and the earth furnishes the return path for the current back to the battery.  That's the way Samuel Morse designed it.  So, if you see a telegraph pole with only one wire on it, that means one circuit was in use.  If you see two wires, that means two Morse circuits.  

I'd much appreciate any information anyone has seen on these topics.  

—Abram Burnett