This is a vintage welsh slate aneroid barometer  & thermometer. The center swivels round to show barometer and thermometer either side.
an instrument used to measure atmospheric pressure to help predict weather changes. 
The device is "aneroid" because it does not use liquid, but rather a sealed metal chamber that expands and contracts with pressure changes. 
The main unit is set within a welsh slate stand.
Measuring, 
16.5cm  wide x 6cm deep x 15cm high
Barometer & thermometer measure
 10.5cm wide x 8cm deep