Liquefied nitrogen, when allowed to evaporate under a pressure of sixty millimeters of mercury, gave a temperature of -214 deg.
"Scientific American Supplement, No. 497, July 11, 1885" by Various
Most of the apparatuses make use of a column of mercury in a U-tube to record the millimeters of pressure.
"Arteriosclerosis and Hypertension:" by Louis Marshall Warfield