barometer in a bell jar
Date: 1850-1900
Inventory Number: 2008-1-0143
Classification: Barometer
Subject:
Maker: American ?
Cultural Region:
Dimensions:
90.5 x 14 cm (35 5/8 x 5 1/2 in.)
Description:
The barometer is very simple, consisting of a spherical vessel with a round foot at the bottom connected via brass fittings to a long vertical glass tube that ends in a brass cap with a screw. There is some mercury inside the glass vessel, but much less than would be needed for it to work as a barometer. The barometer has no scale.
The barometer is kept inside a very tall bell jar that is wide at the bottom and then narrows to be just a bit wider than the barometer's tube that is held inside.
The barometer is kept inside a very tall bell jar that is wide at the bottom and then narrows to be just a bit wider than the barometer's tube that is held inside.
Signedunsigned
FunctionThis barometer is most likely for demonstrational purposes, as it has no scale. It would be used to demonstrate how a barometer reacts to the evacuation of a chamber like the bell jar in which it is kept.
The barometer would have been set up uncovered, so that the mercury would rise inside the column up to the height corresponding to atmospheric pressure (about 760mmHg). If one then placed it inside the bell jar and started to evacuate it with a vacuum pump, the mercury level inside the glass column would move down. In a good vacuum (probably not attainable with this simple system) once evacuated the mercury level in the long tube would be the same as the one in the vessel.
The barometer would have been set up uncovered, so that the mercury would rise inside the column up to the height corresponding to atmospheric pressure (about 760mmHg). If one then placed it inside the bell jar and started to evacuate it with a vacuum pump, the mercury level inside the glass column would move down. In a good vacuum (probably not attainable with this simple system) once evacuated the mercury level in the long tube would be the same as the one in the vessel.