This is a particularly rare and very early mercury barograph by Negretti & Zambra, London, circa 1862. Based on Milne's original design the instrument was developed using mercury as the source of measurement as the aneroid principle was still very much in its infancy. See extract from Knowles Middleton book 'The History of the Barometer'. This instrument is therefore an extremely important link in the evolution of the recording barometer. A very limited number of these have survived the last 160 years and are therefore rarely seen outside of specialist museums. This barograph will make a superb centrepiece for a master collector.