This is an extremely rare, museum quality, mercury recording barometer designed and patented by Antoine Redier and manufactured by Lund and Blockley of Pall Mall, circa 1875. There are two clockwork movements, both working, one turns the recording drum & the other operates the tube to coincide with the rise and fall of atmospheric pressure. The case is in mahogany & the glazed front & solid side panel open up to gain access to the mechanism. A similar, although incomplete example is held by the Science Museum in London. 
Excellent condition.