In the Fortin barometer, the level of mercury in the glass at the bottom of the barometer cistern is adjusted to a scale zero, known as the fiducial point, each time a reading is to be taken. The level of mercury in the column is then read against the scale, using a vernier adjustment for extra accuracy. Air is evacuated from the top of the tube of mercury and the lower end is fixed in the cistern containing the reservoir of mercury. The Fortin barometer is simple to use as it has a clear easy-to-read linear scale. These barometers can be mounted on a wall or suitable pillar.
In addition to instruments manufactured under the Russell Scientific Instruments' name, we manufacture, service and repair F Darton and WF Stanley, Griffin and George, and Gallenkamp precision mercury barometers.
Fortin barometers can be moved without risk of damage but should always be carried flat or upside down. If a Fortin barometer is to be moved after installation, the following procedure must be followed: turn the adjustment screw until the mercury fills the reservoir and the mercury in the column is about 25mm from the top of the scale. Remove the barometer from the wall, incline or tilt gently and then place in a flat position. Finally, adjust the screw further until a small air gap is left in the reservoir. The re-hang the instrument, reverse this procedure.
Please note that all precision barometers are supplied in a purpose-built fibreboard case with a polystyrene cutout inner to support the instrument.
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