A most unusual barometer in having a second temperature measuring device, apart from the alcohol thermometer. At the center is a metallic 340 degree loop, attached to a needle via a toothed arc resting on a gear wheel; as the metal warms up, it will expand and cause the arc to rotate and the needle to move. This is the only one of these I have ever seen, although it is very similar in operation to the French Bourdon bi-metallic aneroid barometer, which has the same arc and gearing, but which was not invented until 1844....and this barometer dates to around 1820.
The main dial is also profusely engraved, as to a lesser extent are the spirit level and the thermometer. The case has finely figured mahogany veneer, on pine, and triple edge stringing of box,ebony, and boxwood. The hygrometer, which is a little deeper than usual, has a cast brass clip holding it in place, instead of the cheaper pressed brass clip.The swan neck top pediment is full depth, instead of just half depth, and the central finial is a nice early one. All of these things add up to indicate a rare and high quality instrument, and one that anyone would be proud to own. As mentioned elsewhere, 10" dial barometers represent only one in twenty of all wheel barometers made, and as such, this is an opportunity to purchase a wonderful, working, scientific instrument