Fortin-type barometer
Date: 1860-1880
Inventory Number: 1998-1-0443
Classification: Barometer
Subject:
Maker: James Green (1808 - 1896)
Cultural Region:
Place of Origin:
Dimensions:
7 x 96 x 7 cm (2 3/4 x 37 13/16 x 2 3/4 in.)
Description:
A mercury barometer consisting of a black metal casing and a glass tube running through the body. The mercury cistern at the bottom is opaque, and the screw underneath it to adjust the level of the mercury inside is now missing.
A screw in the middle of the instrument adjusts the sliding vernier.
There is a thermometer with an accompanying scale underneath the barometric scale.
Barometric scale from 65-82 cm.
Thermometer scale from 0-50 °C, with CENT engraved below the 0.
A screw in the middle of the instrument adjusts the sliding vernier.
There is a thermometer with an accompanying scale underneath the barometric scale.
Barometric scale from 65-82 cm.
Thermometer scale from 0-50 °C, with CENT engraved below the 0.
Signedon brass plate: J. Green N.Y. 2174
FunctionA device for measuring atmospheric pressure. The screw at the bottom of the cistern is now missing, but would have enabled the user to adjust the level of mercury in the cistern to a standard level, and to empty it into the tube during transportation. The mercury that would have been present in the cistern connects to the glass tube running through the instrument. During use, the pressure of the surrounding air acts upon the mercury in the cistern such that it rises to a specific point in the glass tube. This height can then be measured against the scale to indicate barometric pressure. The sliding vernier, adjustable by the center screw allows for more precise measurement of values which are between those marked on the main scale.
The small hoop on top would have been used to hang the barometer from a tripod or from a wall mounting.
The thermometer would have been used to correct the readings for temperatures that varied from the standard.
The small hoop on top would have been used to hang the barometer from a tripod or from a wall mounting.
The thermometer would have been used to correct the readings for temperatures that varied from the standard.