Signedon face: ANDREW J. LLOYD CO. / BOSTON
Inscribedon face, near needle: COMPENSATED/ "Tycos"
FunctionAneroid barometers were used to measure atmospheric pressure and altitude, and were much more convenient than mercury barometers since they did not use any kind of liquid. Instead, a small, partially evacuated and flexible metal capsule inside the casing, which is kept from collapsing by a small spring, contracts and expands in accordance with the surrounding air pressure. The minute changes in the volume of the capsule are translated through internal clockwork to the dial on the face of the barometer, and can be read against the accompanying scales.
One of the major benefits of this kind of barometer was its portability. They could be made extremely small, and were much more easily transported since they did not contain mercury. The downside of their size, however, was the fact that scales had to be considerably contracted in order to fit on the instrument, but extend far enough to be useful.
ProvenanceReceived from R. Novius, Department of Geology, Harvard University.