Thermometers

Today broke the record for the hottest British day on record: +40.3 degrees, just along the road at RAF Coningsby (Mrs C's RAF Cranwell was only +39.95 degrees, so 'significantly cooler'). This Meteorology lessons book shows that the way of gauging the temperature has not changed much since it was written in 1939 during RAF flying training (not my book - I learnt it to qualify as a Meteorological Observer in 1997 and then again during flying training in 2002)...