[LMB] OT: Oxymoronic "AM/PM"

Peter Granzeau pgranzeau at cox.net
Sun Aug 30 17:37:20 BST 2009


At 02:17 AM 8/30/2009, baur wrote:
>question: what system did US railroads use in late 1800-reds, early 
>1900-reds? 

The telegraph.  Specifically, railroads used telegraphs almost from the beginning, independent of commercial telegraph companies.

For that matter, local clocks could be synchronized easily enough:  just observe the time of local noon (the point at which the sun is directly south of the observation location) and apply a correction for latitude or longitude.

For example:  I am one degree 30 seconds west of the meridian which is used for eastern time in the US.  Thus, if I observe local noon, I know that time is actually six minutes after noon EST (an hour is 15 degrees, thus one degree is 4 minutes, and 30 seconds is two minutes).

Every important member of a railroad crew carried an approved timepiece.  I believe their accuracy was supposed to be within 30 seconds a day (they thus needed to be reset and rewound daily), which is pretty good accuracy for a watch movement.  Chronometer movements were supposedly accurate to 30 seconds a month, but a chronometer wasn't carried around in a working man's pocket, either.


--
Pete Granzeau
37º 04' 26" N 76º 30' 08" W 





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