dry and wet bulb thermometers
Date: circa 1930
Inventory Number: 1998-1-0285
Classification: Thermometer
Subject:
Maker: Taylor Instrument Companies (1851 - 1992)
Cultural Region:
Place of Origin:
Dimensions:
21.5 x 11 x 4 cm (8 7/16 x 4 5/16 x 1 9/16 in.)
Accessories: chart "RELATIVE HUMIDITY" in holder stored in file folder
Description:
Two identical thermometers consisting of an unmarked glass tube with a mercury capillary and a spherical bulb for the mercury at the bottom. They are both attached to black metal plates by gold-colored brackets. The black plates have a temperature scale in gold-colored letters, in both cases between 20 and 120 degrees Fahrenheit, although one of them has a few more degrees above the 20 than the other. The metal plates of both thermometers are mounted on a wooden frame side by side with a glass tube between them that starts as a cylinder closed at the top and then narrows and curves towards one of the thermometers having a spherical reservoir underneath one of the thermometers that is open on top. A piece of cloth extends from this reservoir upwards to wrap the bulb of the thermometer.
Signedidentical markings on both plates: Tycos / ROCHESTER, N.Y., U.S.A. / TORONTO, CANADA
Inscribedon back of thermometer base, in pencil: D.P. Wheatland May 13, 1940
FunctionA psychrometer consists of two thermometers placed alongside, one with an exposed bulb (dry bulb), the other covered in cloth and connected by a wick to a water reservoir such that it is always wet (wet bulb).
The thermometer wrapped in the wet cloth will display a lower temperature than the dry one in dry air because the water evaporating lowers the temperature of its bulb. This wet bulb temperature depends on the air temperature and the relative humidity of air (only in a 100% humid air both readings will be the same). One can determine the relative humidity of air with the readings from both thermometers and a table that is now kept in the instrument's file.
The thermometer wrapped in the wet cloth will display a lower temperature than the dry one in dry air because the water evaporating lowers the temperature of its bulb. This wet bulb temperature depends on the air temperature and the relative humidity of air (only in a 100% humid air both readings will be the same). One can determine the relative humidity of air with the readings from both thermometers and a table that is now kept in the instrument's file.