[time-nuts] Setting clocks 100 years ago

[Bob Marinelli]

Hi Murray,

Actually, the ball at Greenwich drops at 1:00 pm every day.  For  
everyone who can get to London, the observatory is well worth at least  
a half day visit, they have several working Harrison clocks and yes  
you can set your wristwatch at 1:00 when the ball drops :) there is  
also a wonderful transit.

Cheers,

Bob


On Nov 4, 2010, at 4:30 PM, Murray Greenman wrote:

> 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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