THE INVENTION OF THERMOMETERS

Placing a kettle full of cold water on the fire is quite an ordinary thing. This time we will 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. Indeed, the boiling water has certainly a much higher temperature than that with which we started our test. However, we need some more exact means of measuring the difference of temperature than the use of 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. The word comes from two Greek words, namely, "thermos" meaning "warm" and "meter," meaning "measure" that is, a measuring instrument.

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 colored liquid. Being very sensitive to temperature changes, Galileo's air thermometer was not sensitive at all to changes of atmospher­ic pressure.

The type of thermometer familiar to everyone at present was first put into general use as early as 1654, or so. Making these first 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 the same number of 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 body as 12°.

Some time later the German physicist Fahrenheit (1686-1736) 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. The latter was worked out by Celsius, a Swedish professor of astronomy. On the Centigrade scale the freezing point of water is marked 0° and the boiling point is marked 100°C, the letter С indicating this scale. This temperature scale is employed in the Our country 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 a wide application in industry.

Exercises

1. Learn the following active words and use them in the sentences of your own:

body (n) тело

boil (v) кипеть

point (n) точка, температура

data (n) данные

freeze (v) замерзать

liquid (n) жидкость

means (n) средство

mer­cury (n) ртуть

pressure (n) давление

rise (n,v) подъем, повышение; повышаться

thermometer (n) термометр