AN EARLY INVENTION.

Auckland Star, Volume LXX, Issue 29, 4 February 1939, Page 3 (Supplement)

AN EARLY INVENTION.

Did -you know that the principle of the earliest thermometer, one invented in 1607 bv the Italian astronomer Galileo, lias been m use for more than 300 years ?

Galileo's original invention was an air thermometer, but later lie improved the idea by using alcohol for gas. And this improved method has been in use ever

The principle of tlie early thermometer was tlie samp a§ that used in most thermometers of to-day.

When coloured alcohol, for instance, is conlined .in a slender glass tulip the difference of expansion, indicated by tlie height at which it stands, gives u-s the temperature..

As a substitute for alcohol mercury is used in most thermometers because it has a rather high boiling point and low freezing point, and uniform expansion when it is warmed.

Ordinary thermometers arc made by filling, with mercury or coloured alcohol, a glass bulb provided with a slender glass tube. The heafe is applied until the mercury flows, then the top of the tube is scaled by melting the glass.

As it cools the mercury contracts, leaving an almost perfect vacuum ill the upper part of the tube. When the thermometer has become normal, after the heating and cooling process,- a scale for reading the changes in the temperature is marked. On a strip of metal or porcelain used for backing, or on the glass itself, you will find the figures by which we. read the temperature.

There are special instruments for taking exceedingly high temperatures. They are gas and electric thermometers, and are known as "pyrometers."

Doctors have a special kind called -clinical thermometers." With these they take your temperature when you are ill, to see whether you have fever.