The history of the thermometer Placing a kettle full of cold water on the fire is quite an ordinary thing. This time we shall do it to carry out a simple experiment. Placing a finger into the kettle from time to time, we find that the water is gradually becoming hotter and hotter, until it boils at last. In scientific language we describe this phenomenon by saying that the temperature of the water is rising. However, we need some more exact means of measuring the difference of temperature than our finger. In effect, the finger can give us neither exact information, nor numerical data.
As a matter of fact, the very first step in the development of heat engineering made it necessary to find a device for indicating temperature and for measuring its changes. As is well known, the thermometer is the very instrument that serves this purpose.
As early as 1602, Galileo invented an air thermometer. It consisted of a glass bulb containing air and connected to a glass tube, the latter being immersed into a coloured liquid. Galileo's air thermometer was sensitive not only to temperature changes but also to changes of atmospheric pressure.
The type of thermometer familiar to everyone at present was first put into general use as early as 1654. Making the first measuring instruments was not an easy thing at all. Needless to say, the most difficult problem of all was that of marking the degrees on the thermometer, in other words, of graduating the scale. It was decided, at last, to take two fixed points and to divide the interval between them into small equal parts or degrees. And then, in 1701, Isaak Newton, the famous English scientist, whose name is known all over the world, constructed a scale in which the freezing point of water was taken as zero and the temperature of the human j body as 12°.
Some time later the German physicist Fahrenheit proved that the temperature of boiling water was always the same at the same atmospheric pressure. It might therefore be used as a second fixed point instead of the temperature of the human body. As for the liquid used, it was mercury which has been mostly employed since that time.
On the Fahrenheit scale the boiling point of water is taken as 212° and the freezing point as 32°, the interval being divided into 180 equal parts. The scale under consideration is indicated by writing the letter F after the temperature, as for example, 212°F. This scale is mainly used in English-speaking countries.
So far we have not mentioned the Centigrade scale. On the Centigrade scale the freezing point of water is marked 0°C and the boiling point is marked 100°C, the letter C indicating this scale. This temperature scale is employed in the Russia as well as in most other countries of the world.
Speaking of thermometers, one must make reference to the pyrometer. We know of its being used for measuring temperatures that are too high for mercury thermometers. We also know of its finding wide application in industry.

I. Fill in the blanks with the word from the box.
Degrees, indicated, liquid, purpose, body, freezing point, put into use, boil, data, the latter, difference, means, mercury, pressure, rises.
1. What is the … of this laboratory work?
2. These … were used in research work.
3. We … water to produce steam.
4. At what temperature does this … boil?
5. The … of water depends on atmospheric pressure.
6. It is important to know the quantity of energy present in a … .
7. Steel melts at 1300 … .
8. What is the … between potential and kinetic energy?
9. What is the… of water?
10. The capacity of the generator is … in the instruction.
11. Coal and uranium are fuels, … is used in nuclear reactors.
12. A lightning conductor is a … of protecting houses from lightning.
13. … is a metal.
14. What is the atmospheric … today?
15. A new reactor was … .
16. When the body is heated its temperature … .
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