Casella CEL Fortin barometer - Manual (Page 3)

HB3121
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INTRODUCTION
The Fortin barometer is the most widely used type and can be found in many
industrial laboratories, workshops, classrooms and meteorological offices.
The measurement of atmospheric pressure finds its greatest use in meteorology,
where knowledge of the pressure distribution over a very wide area at the same
moment is of vital importance in the forecasting of weather.
PRINCIPLE OF OPERATION
As atmospheric pressure changes the mercury level in the cistern changes
accordingly, for example, an increase in pressure will cause the mercury level to
drop. The Fortin barometer allows the mercury level in the cistern to be set to a
fixed datum or zero every time a reading is taken. The mercury is contained within
a flexible pouch and a screw jack causes the level to either rise or fall. Having
made this setting the top of the column is then measured by bringing the lower
edge of the vernier so that it apparently just touches the top of the column. The
reading is then taken on one or other of the scales provided.
PACKING
Since all mercury barometers are delicately constructed it is important that proper
care is taken to prevent damage during all stages of handling. To help in this, a
barometer is packed with its cistern uppermost in a specially designed case, which
must be kept as near vertical as possible.
WARNING
Mercury is Toxic and corrosive. It should be treated with caution avoiding contact
with skin.