What do we call the instrument
For measuring gas? A gas-meter
For measuring electricity? An electrometer
For measuring speed of a motor? A speedometer (speed-meter)
For measuring the distance a bicycle travels? A cyclometer (cycle-meter).
In each case what does "meter" mean? It means an instrument for measuring. What name may I give to an instrument for measuring heat? You may call it a heat-meter.
Tell the pupils that, in science, many Greek words are used, and that you will put a Greek word in place of the English word "heat", namely "thermos", as in thermos bottle. What will the name become? Thermosmeter, or thermometer.
3. Practice in using thermometers:
The unit of measurement (degree) should be given, and the scale taught from the black-board. Thermometers may then be given to the class to examine and use.
Saucepans having white inner surfaces are best to use for the experiments, as changes made by the heat are more plainly seen.
Observations of water under heat:
(1) At a temperature of about 100 degrees, very small bubbles form at the bottom and sides of the dish and rise slowly to the surface of the water. These bubbles are a film of water containing the air that was in solution, which, when expanded, rises to the top of the water.
(2) At a temperature of about 180 degrees, a few larger bubbles form at the bottom of the dish and rise slowly to the surface of the water, making a slight movement in it. In these bubbles air is replaced by steam which is formed from the water by the heat.