Early 20th century bronze Heliochronometer
Negretti and Zambra on stone pedestal
extremely precise forms of sundial
capable of accuracy within one minute
assuming it is in sunlight.
Invented at the end of the 19th
century with the introduction of
Greenwich Mean Time in Britain.
Up until this time each major city in the UK had its own local time
with the expansion of the railway network a standardised time
The heliochronometer is calibrated with months and
to enable it to mathematically calculate the "Equation of Time"
compensating for the earths elliptical rather than circular
orbit of the
sun which would otherwise result
in sundials being up to fifteen minutes
fast or slow
depending on the time of year.
49" (125cms) High
detailed photograph of dial click image