Cistern

{
  "id": "MLC-T-MET-004316",
  "term": "Cistern",
  "field": "Meteorology and atmospheric science",
  "definition": "The reservoir at the base of a mercury barometer that contains the pool of mercury into which the open end of the glass tube is placed. The surface of the mercury in the cistern serves as the lower reference point for measuring the height of the mercury column, which rises and falls in response to changes in atmospheric pressure. In a Fortin-type barometer, the level of the mercury in the cistern can be adjusted to a fixed zero point before each reading.",
  "see_also": [
    "cistern barometer"
  ],
  "url": "https://mlchart.com/terminology/meteorology/cistern/"
}