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I had been wondering why chronometer rates were being checked when
accurate time was available over the cable.  One hypothesis was that
the cable was broken, so accurate time was not avaiable.  To determine
this, I examined the original cable-repair story
(http://atlantic-cable.com/Article/Combe/).  In many cases, the sights
were being taken when the cable was operating.  In the first case, the
Cadiz-Teneriffe cable was broken, but they were taking time sights at
the Cadiz











                                                           end, where
accurate time should have been available from the Spanish land line.
After repairing the Cadiz-Teneriffe line, they again took time sights
in Cadiz.  In the second case, they checked their chronometers after
finishing the repair of the Teneriffe-Cape Verde cable.  There also was
a chronometer check in Teneriffe when the Cadiz-Teneriffe cable was
still broken.

It may be that time signals were not available at the proper time.
After reading the wonderful link provided by Paul Hirose, it is clear
that competent people were required to transmit telegraph time signals.
For the cable repair vessels, there also were competent people on board
ship to perform a direct check.  It is clear that the longitude of
important places such as Cadiz and Teneriffe would have been
established carefully at the time of this story.

The wonderful link provided by Paul Hirose indicates that
telegraph/cable time checks were encountering delays due to the speed
of light over long distances.  But also suggests that transmission
times were nearly instantaneous.  I guess relays close fast enough that
the accumulated delay from them was insignificant.

   

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