Description
A thermometer is an instrument that measures how hot or cold something is, in other words, its temperature. Most familiar is the "Mercury-in-glass" thermometer, but there are many other kinds.

Many materials expand as they get hotter and contract as they get colder. This expansion and contraction can be used to measure the corresponding changes in temperature. Thus the first useful thermometers were made from a glass bulb full of mercury to which was attached a narrow glass tube. As the bulb is heated, a fine thread of mercury expands up the narrow tube. Thermometers, requiring great skill in glass working, were first made by Daniel Fahrenheit of Amsterdam in 1717.

To measure temperature precisely, a numerical scale of "degrees" is needed. To provide this scale two fixed points are chosen, such as melting ice and boiling water. Convenient temperatures are then given to these two fixed points: today melting ice is given a temperature of 0 degrees and boiling water 100 degrees. This is the Celsius or Centigrade scale (although it is quite arbitrary). Fahrenheit himself originally chose the coldest temperature that he could produce (a freezing mixture of ammonium chloride and snow) as 0 degrees and body temperature as 96 degrees. This resulted in the Fahrenheit scale in which the freezing point of water is 32° F and the boiling point of water is 212° F.

01/03/2001
Created by: Chris Lewis on 01/03/2001