| Weather Term | Description / Definition |
| Inches of Mercury | (or in Hg) Unit of atmospheric pressure used in the United States. The name comes from the use of mercurial barometers which equate the height of a column of mercury with air pressure. One inch of mercury is equivalent to 33.86 millibars or 25.40 millimeters. See barometric pressure. First divised in 1644 by Evangelista Torricelli (1608-1647), an Italian physicist and mathematician, to explain the fundamental principles of hydromechanics. To convert millibars (mb) to inches of mercury (in Hg), divide the millibar reading by 33.86: in Hg = mb / 33.86 |