The whole is enclosed in a jacket connected with a boiler containing a liquid, the vapour of which serves to keep the inner tube at any desired temperature.
The temperature at different heights was measured by iron wires forming thermo-junctions with the mercury in the inner tube.
Through this space the fresh surface water finds its way, and dissolving the salt below rises in the inner tube as brine, but only to such a level that the two columns bear to one another the relation of ten to twelve, this being the inverse ratio of the respective weights of saturated brine and fresh water.
The inner tube H is movable, making a change in the length of the tube possible.
As a rule this inner tube has a mark which allows the length of the tube to be set.