[time-nuts] Selling time to the railroad

Brooke Clarke brooke at pacific.net
Sat Nov 1 17:25:31 EDT 2014

Hi Howard:

 From what I know the USNO used a Photographic Zenity Tube that made use of a pool of Mercury and glass plate that was 
exposed 4 times for a single star meridian crossing.  The plate was then read using what amounts to a microscope and 
large X-Y table and after doing some math the exact time (within a millisecond or so) of the meridian crossing could be 
determined.  Since the exposure was based on the observatory sidereal clock the answer was in sidereal time.  This 
nighttime activity is needed to maintain the observatory clock.

I suspect that the source of local time would be one of the ticks from the sidereal clock.  So providing the noon or 
hourly time ticks is a different activity.
Mail_Attachment --
Have Fun,

Brooke Clarke
Howard Davidson wrote:
> The physics department at the little Liberal Arts college  I went to in Iowa, Grinnell college, used to sell time to 
> the Rock Island Railroad. We had two excellent pendulum clocks that back when this was in action, were synchronized to 
> zenith crossings of particular stars. This was a manual operation performed by undergraduates who were paid to be up 
> at weird hours of the night. The time ticks from the clocks were transmitted to the Rock Island station in town 
> electrically. I presume they distributed it by telegraph.
> hld

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