[time-nuts] Setting clocks 100 years ago

Dave Brown tractorb at ihug.co.nz
Fri Nov 5 11:37:43 UTC 2010


Another existing sample of a time ball station close to home (for me) 
is here in Lyttelton near Christchurch, NZ (quake city)
http://www.teara.govt.nz/en/timekeeping/2/3
 It too suffered some building damage in the recent seismic event but 
will no doubt be restored in due course.
  Worth a look if you're ever out this way.
 DaveB, NZ

----- Original Message ----- 
From: "Murray Greenman" <Murray.Greenman at rakon.com>
To: <time-nuts at febo.com>
Sent: Friday, November 05, 2010 12:30 PM
Subject: [time-nuts] Setting clocks 100 years ago


> Navigators used chronometers to determine their longitude. If they 
> were
> stopped in one place long enough, they could work out longitude by a
> complicated process of star and lunar observations; however, when 
> they
> left an established port, they usually took with them a time 
> standard
> based on local measurements of the sun and the known location of the
> port.
>
> These measurements used a device called a 'Transit', which was a 
> simple
> telescope mounted so that it pivoted in elevation, but was fixed N-S 
> in
> azimuth. Midday was marked by the time at which the sun transited 
> the
> telescope. It thus had higher resolution than a sundial. Getting N-S
> axis correct involved determining by iteration and surveying the 
> axis
> that gave maximum elevation at time of transit.
>
> Once the transit was observed, a large ball on top of the building 
> was
> dropped, indicating midday, and in some locations a cannon was also
> fired. Ships in port could observe the ball drop and hear the 
> cannon. To
> this day the ball drops at midday at Greenwich.
>
>
> 73,
> Murray ZL1BPU
>
>
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