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


Blogger CPRR Discussion Group said...

The Western Pacific Report of Commissioners on 4th Section (last section, Altamont to Farwell) dated Jan 20, 1870, (similar constrution style to the final part of the CP) describes the telegraph line as "not less than thirty redwood poles to the mile; size at bottom eight by eight inches, at top four by four inches, length twenty six feet, an they are set to a depth of four feet in the ground. No. 9 galvanized wire is used. The office instruments are of the very best quality, of the most approved style and are funished by the best manufactureers. And we certify that it is first class."

Randy Hees

7/24/2005 5:18 PM  
Blogger CPRR Discussion Group said...

From: "Larry Mullaly"

I cannot speak for the type of wire used on the original Central Pacific. But on the Southern Pacific between Goshen and Yuma California, the telegraph line is described in US Railroad Commissioner reports as strung with “Number 9 galvanized wire.”

Larry Mullaly

7/24/2005 5:21 PM  
Blogger CPRR Discussion Group said...

From: "Mullaly, Larry"

I found the following source, originally published in 1870 as the "Modern Practice of the Electric Telegraph." I have not yet found signs of telegraph relay practice, but hope springs eternal!


7/25/2005 1:43 PM  
Blogger CPRR Discussion Group said...

Our webpage about the CPRR Brooks August 6, 1867 Patent Telegraph Insulator has many additional telegraph resources linked.

7/25/2005 1:45 PM  
Blogger CPRR Discussion Group said...


I'll try to answer your questions and then ask a couple.

1) The railroad used iron wire. Copper wire would have been too expensive until late in the century.

2) The poles were square cut with a cross arm that had two expensive Brooks insulators each. These were later replaced with the more common glass insulator. Physical remnants of the poles, insulators and wire have been found in the Promontory vicinity. The poles, wires and insulators have been replicated at Golden Spike NHS. Photographs of remnants are in the book mentioned the other day.

3) Can't answer this for day to day operation. But for May 10, the CP working with Western Union, it appears, had "through" lines since the "blows" were reported immediately across the nation. Relayed messages may have been more the rule along the line, since batteries are mentioned in various locations along the UP at least. A battery, telegraph key, and table under the weather are mentioned as the first things placed by the UP at Promontory – primarily to watch the CP's movements.

Couple questions, and maybe you are already onto this. How many batteries or cells would be needed at Promontory to send the May 10 message? The Western Union line was not completed to Promontory at that time, so don't know the equipment used other than CP invoices state telegraph equipment came from William Lundberg and Charles F. Marwedel of San Francisco. Do you know anything about these manufacturers?


Bob Spude – Historian – Cultural Resources Management – National Park
Service – Intermountain Region – 505.988.6770 Voice – 505.988.6876 Fax

The National Park Service cares for special places saved by the American people so that all may experience our heritage.

7/25/2005 3:59 PM  
Blogger CPRR Discussion Group said...

Here are some photographs of a Telegraph Yard Arm with Brooks Insulators, and a Telegraph Insulator Fixture to Attach to a Tree.

7/25/2005 4:05 PM  
Blogger CPRR Discussion Group said...

The following images show telegraph lines:

1) Watkins Cape Horn cabinet view.
2) Hart stereoview #56.
3) Carbutt stereoview, "Westward, the Monarch of Capital Makes its Way."
4) William H. Jackson view of Engine No. 86 at Green River Station. Wyoming.
5) Hart stereoview of "Fort Point Cut on the Central Pacific R.R. — 70 feet deep and 600 feet long."
6) Hart stereoview of the depot at Truckee.
7) Savage stereoview, 1000 mile tree.
8) Savage stereoview, Echo City.
9) Weitfle stereoview #418.
10) Hart stereoview #322.
11) Hart stereoview #355.
12) William H. Jackson, Promontory.
13) A.J. Russell, Imperial View, "Laying of Last Rail."
14) Hart stereoview #357.

7/25/2005 6:42 PM  
Blogger CPRR Discussion Group said...


Nice compilation. The [other] link has a brief piece on the Brooks patent "ramshorn" insulators used on the CP.

Bob Spude – Historian – Cultural Resources Management – National Park Service – Intermountain Region ¨ 505.988.6770 Voice – 505.988.6876 Fax

The National Park Service cares for special places saved by the American people so that all may experience our heritage.

7/25/2005 6:45 PM  
Blogger CPRR Discussion Group said...


I have been trying to fathom how "the Fathers" operated the Morse Telegraph wire from Promontory to Sacramento, 690 miles, when they sent the "Done" message on May 10,1869. Too bad the Fathers left us no account of how they did it, so we will have to guess.

Many problems enter into the calculations.

First the wire. Resistance of #9 galvanized iron telegraph wire is today given as about 11 ohms/mile, but Pope's Electric Telegraph Handbook of 1881 gives it as 16 ohms/mile (a whopping 69% difference.) We know for certain there have been metalurgical changes in the manufacture of wire since its first use in electromagnetic circuits in the 1830s, which have changed its electrical properties. All wire is not created equal.

Second, the batteries. In those days, the only source of electricity was the "primary battery" or "gravity cell" made in open top round glass jars 6-8" tall and 9-10" diameter, of about one gallon capacity. Into each "cell" of this battery went a chunk of copper weighing several pounds, a chunk of zinc weighing several pounds, a dozen ounces of bluestone copper sulphate, several ounces of sulphuric acid, and water. Each cell gave a whopping output of 1 volt (yup... that's ONE VOLT.) The zincs lasted perhaps three months, the coppers a bit longer. If you needed 12 volts, you needed 12 of these cells, and so on.

Third, the telegraph instruments. I believe the telegraph relays (receiving instruments) were wound to 150 ohms resistance and designed to operate at a line current of 0.050a (50/1000ths of an amp.) I tested one and found that it will function acceptably down to an operating current of 0.040 amp and follow hand sending (which isn't fast,) so I use 0.40 amp as a "minimum threshold" for operation of Promontory's telegraph line.

Now to the big picture. A 690 mile line (Promontory - Sacramento) would have had at least 7,890 ohms resistance, and that's with only one telegraph instrument at each end and none of the intermediate towns "cut in." Operating such a line would have required 394 volts. That means 394 of those "gravity battery" cells! Ouch. Add a bunch of stations in the middle, and the voltage goes up even further.

Therefore, I conclude that the line was probably operated in segments (like the first transcontinental telegraph wire, opened in 1861,) with manual re-transmission of messages being necessary at the intermediate points. I made a wild guess that the segments were Promontory-Carlin, Carlin-Wadsworth, Wadsworth-Sacramento. On Golden Spike Day, the telegraph relays could have been temporarily rearranged at the intermediate points (Carlin and Wadsworth) so that each section of the wire "repeated into" the adjoining section to the west, and so"worked through" back to Sacramento, with Sacramento hearing the clicks right as Sanford, Dodge and others hammered on the spike.

Assuming this "three segment" theory, and assuming some intermediate stations had equipment (relays) cut in on the wire, here are the voltages required to operate the three segments. The lower voltage given is that required to operate the line at "minimal threshold"conditions (0.040a,) and the higher voltage given is that required to operate the line as designed (0.050a.) (The calculations also assume 11 ohms/mile for #9 galvanized iron telegraph wire.)

Promontory to Carlin, 264 miles, with 4 intermediate stations cut in: 156v to 195v needed.

Carlin to Wadsworth, 255 miles, with 5 intermediate stations cut in: 166v to 208v.

Wadsworth to Sacramento, 189 miles, with 10 intermediate stations cut in: 167v to 209v.

(By comparison, the first transcontinental telegraph line (1861) had one segment almost 590 miles long, Omaha to Fort Laramie, which would have required 307v to 384v.... very hefty for pre-Civil War technology!)

One can see by these numbers that the telegraph line was of some complexity and could not have been cheap to construct or operate. Can you imagine maintaining 200 liquid battery cells in, say, the Carlin station? But it was far superior to the Pony Express or carrier pidgeons!

Oh, in case you're wondering how long the nation's communications continued to rely on those one-volt-per-cell gravity batteries... Four decades after Promontory the biggest of the Western Union offices were switching to dynamo-charged storage batteries, but the faithful old gravity cell mustered on in smaller railroad offices well into the 1950s.

—Abram Burnett,
Old Brass Pounder

8/01/2005 8:02 PM  
Blogger CPRR Discussion Group said...

Electromechanical relays (switches activated by electromagnets) were used into the 1960's for telephone switching and computation (for example, the IBM 407 accounting machine).

Reading your discussion of telegraphy made me realize for the first time why they were called "relays" – they were automatic mechanical devices which operated as amplifiers to relay the telegraph signal, substituting the higher voltage of a local set of batteries outputted along the telegraph line, for the diminished incoming voltage of the arriving message from the previous station. (A function now performed by transistor amplifiers; relays being used today almost exclusively for high power circuitry – no longer for communications or calculation.)

Joseph Henry invented the electrical relay, a means of transmitting electrical impulses over long distances in 1835. The relay serves as the basis for the telegraph.

It seems that electromechanical relays were used for long distance telegraphy by the mid-19th century.

A detailed chronology of the development of electromechanical telegraph relays could be compiled by examining 19th century patents.

8/01/2005 8:30 PM  
Blogger CPRR Discussion Group said...


... does anyone know how long Morse Telegraph lasted on this great piece of railroad?

—Abram Burnett

8/01/2005 9:13 PM  
Blogger CPRR Discussion Group said...

From: "Larry Mullaly"

Your telegraph information is very interesting. I have not done any close reading on the topic, but what of the possibility of automatic repeater units?

Also, the division points along the road would be the logical place for relay points, done manually or automatically if that was possible.

In 1879, on the transcontinental route the division points were at

Oakland Wharf mp 0
[Lathrop mp 83]
Sacramento mp 103
Truckee mp 239
[Wadsworth mp 329]
Winnemucca mp 464
[Carlin 584]
Wells mp 664
[Terrace mp 759]
Ogden 883

On the great stretches across Nevada, possibly the crew district/engine servicing points shown in brackets may have been the breakpoint for shorter dispatching territories.But this would put half the operations outside the immediate oversight of the division superintendent, something I doubt very much.

I have train order log information from 1878 and this shows Oakland Wharf transmitting train orders across all the territory between there and Sacramento [103 miles]. The practices used for train dispatching would (in my mind) rule out any intermediate relay points within a division.


8/02/2005 7:32 AM  
Blogger CPRR Discussion Group said...

From: "Kevin"

It seems to me that the book(s) by Kay Fisher covering the respective career of herself and her husband as wife/cook and signal/telegraph maintainer on the SP in and around Donner Summit makes some mention of how long Morse telegraphy was used on this portion of the Overland Route. It is a specific subject not well covered and overdue for some scrutiny.


9/01/2005 9:40 AM  
Blogger CPRR Discussion Group said...

See related discussion.

8/06/2013 8:25 AM  

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