What is a Round Aneroid Barometer?

The first aneroid barometers were made under patent, which was granted 1844, by Vidi.  These were sold by E J Dent in London and like most new inventions they were first thought not to be anywhere near as good as the mercury barometers.  However, on board ship their importance was readily recognised, as instead of breaking many tubes as the ship rolled against the heavy seas, the aneroid was far more sturdy and could be screwed down to the captain's table or desk, similar to the chronometers.   These early ones were invariably in brass cases, approximately 4 ½" in diameter, and were sold under licence by E J Dent, sometimes with other retailers names, but they were all supplied through E J Dent until the patent ran out around 1852.  After the patent run out after 1852 many brass case barometers were copied, some were made to be held on semi-circular wooden stands.  These aneroid barometers can easily be adjusted for altitude by use of a suitable screwdriver on a screw at the back of the case. They mostly have silvered brass dials, but occasionally card dials are also encountered.  From these many types of aneroid barometers, round ones of different sizes were produced.  Most early ships ones would have been in wooden cases, secured by a locked lid and laid flat on a desk.  The later ones for ships often had two or even three hanging points to secure on bulkhead.   Many were made and sold cheaply by the RNLI for fishermen's safety.  For domestic purposes many were also made of different sizes, often in decorative wooden cases, some inlaid.  They varied in their dial material from engraved brass to cardboard to porcelain, white glass and later ones of the 1920s with aluminium.  Occasionally within this group you can find a Bourdon type of barometer, which is an unusual type of aneroid which uses a horse-shoe shaped capsule and the ends move closer or further apart according to the pressure and the linkages transmit this to a hand.Bourdon barometers are quite uncommon and mostly come in brass cases, sometimes on wooden stands.