On 27/06/2019 09:23, tony sayer wrote:

Much has been written re the long term temp variation of the climate but
as it appears were talking about around 1 deg C change over quite a long
time, pre industrial era, just how absolute accurate where the
thermometers in use?.

Course these days there are some very accurate ones around but back then
in the 1800's how accurate was a standard one back then anyone any
idea?.

By about 1850 Negretti & Zamba had perfected weather thermometers that
were almost as good as the ones we have today. Their centenary catalogue
is online. Their best antique kit sells for good money at auction.

https://web.archive.org/web/20110719...retti_cent.pdf

Fitzroy was instrumental in getting their kit widely distributed and
used to help try and save lives at sea by warning of impending storms.

You can find complaints from the astronomer royal about the failings of
earlier kit (mostly failure to automatically record data reliably rather
than of calibration). Calibrating between melting ice and boiling water
was fairly reliable if you measure the atmospheric pressure.

https://www.ebay.co.uk/itm/VICTORIAN...AOSwZVpck~i r

Lets not take into account as to where the measurement was made either
in town out in the country at the sea side etc, but the gear in use to
measure?.



--
Regards,
Martin Brown