Henry J Green Observatory Barometer
This is a Model 2 Observatory Barometer in working condition, made by the Henry J Green Company in Brooklyn, New York, USA.. It's a Fortin barometer. The barometric pressure scale ranges from 25.7 to 32.8 inHg and is divided into twentieths of an inch allowing mercury column measurement with the vernier scale to 1/500th of an inch. It also has a scale and vernier scale for measurement in millibars. It was usable to an altitude of about 4,000 feet above sea level. The mercury tube bore is 0.25 inches. The mercury thermometer ranges from 4 to 124 degrees Fahrenheit, with an equivalent Celsius scale.
The instrument is shown in the circa 1915 Henry J Green catalog available elsewhere on this website but I suspect that this is newer based on its excellent condition. The unit of millibars was introduced in the UK in 1909. Inside the door is the original corrections chart for adjusting the mercury column height to local pressure. It works well.
The instrument is shown in the circa 1915 Henry J Green catalog available elsewhere on this website but I suspect that this is newer based on its excellent condition. The unit of millibars was introduced in the UK in 1909. Inside the door is the original corrections chart for adjusting the mercury column height to local pressure. It works well.
The military version of this barometer is the ML-2 mercury barometer also made by Henry J Green. The 1944 US War Department technical manual for the ML-2 may be downloaded below (72 pages):
From 1954, US Army Manual TM 11-428, "Barometers ML-2 through ML-2H and Cases", may be downloaded below (84 pages):
