Water thermometer
Wa"ter ther*mom"e*ter\ (Physics) A thermometer filled with water instead of mercury, for ascertaining the precise temperature at which water attains its maximum density. This is about 39[deg] Fahr., or 4[deg] Centigrade; and from that point down to 32[deg] Fahr., or 0[deg] Centigrade, or the freezing point, it expands.