hypsometer

A Hypsometer is an instrument for measuring height or altitude. Many different physical principles may be used.

A simple scale hypsometer allows the height of a building or tree to be measured by sighting across a ruler to the base and top of the object being measured, when the distance from the object to the observer is known.

A pressure hypsometer as shown in the drawing (right) employs the principle that the boiling point of a liquid is lowered by diminishing the barometric pressure, and that the barometric pressure varies with the height of the point of observation.

The instrument consists of a cylindrical vessel in which the liquid, usually water, is boiled, surmounted by a jacketed column, in the outer partitions of which the vapour circulates, while in the central one a thermometer is placed. To deduce the height of the station from the observed boiling point, it is necessary to know the relation existing between the boiling point and pressure, and also between the pressure and height of the atmosphere.

Modern hypsometers use the combination of a laser rangefinder and a clinometer to measure distances to the top and bottom of objects, and the angle between the lines from the observer to each to calculate height.

References

• This article incorporates text from the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.