This is a beautiful fully restored combined barograph &  thermograph by the world renowned makers, Negretti & Zambra of London, circa 1938. Originally manufactured for commercial use with a metal case the instrument now has a rich re-polished oak case with a lift off lid and deep bevelled glass all round. There is a 23mm diameter circular hole in the centre of the small panel at the right hand end to allow the air circulation for more accurate temperature readings. At the base of the case is a chart drawer with hardwood bun feet below.
The diaphragm set within the barograph movement is the advanced version developed and patented by the makers in the 1930s and was considered at the time to be more accurate under all types of external environment than traditional movements. The thermograph sensor is of the bi-metallic coil design.
Both original pen arms are engraved 'Barograph' and 'Thermograph' and there are two separate ink bottles - red for barometric pressure and green for temperature. The whole movement has been designed so that both traces record on the chart and the pens freely pass each other .
The brass movement has been stripped, cleaned and re-polished
A quantity of the correct dual recording charts are included together with two bottles of coloured ink. A copy of a reprinted pamphlet describing operating instructions and interpretation of barometer trends is also included.