The Collaborative International Dictionary of English v.0.48:

cryometer \cry*om"e*ter\, n. [Gr. ? cold, frost + -meter.]
   (Physics)
   A thermometer for the measurement of low temperatures, esp.
   such an instrument containing alcohol or some other liquid of
   a lower freezing point than mercury.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

cryometer
    n 1: a thermometer designed to measure low temperatures