Measuring temperature
For thousands of years, people judged the temperature by how they felt.
To check the heat of an oven, cooks put a hand into the oven. If the
weather felt cold, people put on more clothes.
Long, long ago, the Aborigines of Australia wore little, if any,
clothing. If it was cold at night, they simply curled up with one or
more of their dogs. According to a story which may or may not be true,
these people “measured” the temperature by the number of dogs they
needed to keep them warm! A “one-dog night” might be a little chilly. A
“three-dog night” was, of course, much colder.
There was no way to measure temperature until the invention of the
thermometer (thuhr [mahm]{.smallcaps} uh tuhr) about 400 years ago.
A Swedish astronomer, Anders Celsius, was the man who developed the
Celsius system for measuring temperature.
About 300 years ago, a German scientist named Fahrenheit
[(far]{.smallcaps} uhn hyt) built the kind of thermometer that we use
today. The word thermometer means “heat measure.”
Fahrenheit’s thermometer was a closed glass tube with a bulb at one end.
The bulb was filled with mercury. When the mercury was warm, it would
creep up the tube. When it was cool, it would drop back down toward the
bulb.
To measure temperature, Fahrenheit needed a scale, or series of marks,
on the glass tube. When he put the thermometer into a mixture of ice and
salt, the mercury went nearly all the way down the tube. So, Fahrenheit
put a mark on the tube at this place. He called this point zero degrees,
or 0°.
Now he needed a high point. On some other temperature scales, the heat
of the human body was marked at 12. But Fahrenheit had a very exact
thermometer, and a scale of 0 to 12 was not great enough. He multiplied
the 12 eight times and used 96 for his high point. That was close to the
actual body temperature of 98.6°.
Using this scale, he found that the freezing- point of water was 32
degrees. After extending the scale higher, he found that the boiling
point of water was 212 degrees.
Today, people in most parts of the world use a thermometer that has a
different scale. This scale, part of the metric system, is called the
Celsius [(sehl]{.smallcaps} see uhs) scale after the Swedish astronomer
who worked it out. On the Celsius scale, 0 is the point at which water
freezes. This is the same as 32 degrees on the Fahrenheit scale. And on
the Celsius scale, the boiling point of water is 100 degrees. This is
the same as 212 degrees on the Fahrenheit scale.
