an instrument, invented by Edison, for measuring very minute variations of pressure, temperature, moisture, etc. It is founded on the discovery of the inventor that carbon, when pressed in the form of a button, affects the electric currents passing through the same, and offers a resistance which diminishes with the pressure. So sensitive is the carbon that, when this pressure varies to the amount of one millionth part of an inch, the variation in the electric current passing through it will cause a proportional deflection of the galvanometer needle. The practical uses of the instrument are said to be: (1) Warning to vessels of the approach of icebergs, by exposure to the air or to the water cooled by their vicinity; (2) Indicating otherwise inappreciable weights; (3) Recording pressures of air in motion, thus affording a useful addition to the anemometer.
Entry from Everybody's Cyclopedia, 1912.