thermobarometer

from The Century Dictionary.

• noun A thermometer which indicates the pressure of the atmosphere by the boiling-point of water, used in the measurement of altitudes.
• noun A siphon-barometer having its two wide legs united by a narrow tube, so that it can be used either in its ordinary position as a barometer or in the reversed position as a thermometer, the wide sealed leg of the barometer then serving as the bulb of the thermometer.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Physics) An instrument for determining altitudes by the boiling point of water.
• noun A siphon barometer adapted to be used also as a thermometer.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun obsolete, physics An instrument that measured altitudes via the boiling point of water
• noun geology A mineral used to estimate temperature and pressure in the rocks during its formation