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" <[email protected]>
To: <[email protected]>
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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