Two manometers filled with coloured liquid, the long limbs of which are carried upwards quite parallel. A scale graquated in half centimeters admits of easy reading. A second scale is at the back. The sharter limbs of the manometer are cut off by wider vessels each having a cock and an attachment for rubber tubing. By means of the rubber tubing the sensitive air capsules (receivers) are connected with the manometers.
Used for a large number of experiments on heat, electricity etc.

See also: http://physics.kenyon.edu/EarlyApparatus/Thermodynamics/Differential_The...