Maureen Baghurst, age 12, of Poughkeepsie, N.Y., for her question:
WHO INVENTED THE THERMOMETER?
A thermometer is an instrument used to measure temperatures, with the most common type being the mercury in glass tube used in homes to test body warmth. The first thermometer was made almost 400 years ago in 1593 by Galileo, the famous Italian astronomer, mathematician and physicist.
Galileo's instrument was called a "thermoscope," and it wasn't very accurate.
The first accurate thermometer came along in 1641 and was an instrument that used alcohol. In 1714 it was further improved by German physicist Gabriel Fahrenheit who came up with the type of mercury thermometer that is still in use today.
Fahrenheit also developed the Fahrenheit temperature scale. He determined three fixed temperatures: zero degrees for the freezing point of salty water, 32 degrees for the freezing point of pure water and 96 degrees for the normal temperature of the human body. (Later experiments, by the way, proved the body's temperature to be 98.6 degrees Fahrenheit.)
The Celsius scale was the result of the work of Swedish astronomer Anders Celsius. He came up with the plan in 1742, but it was changed and improved a few years later. On the Celsius scale, zero degrees is the freezing paint of pure water and 100 degrees is the boiling point.
A liquid in glass thermometer works on the principle that liquids increase in volume as their temperature rises. The mercury in glass type is made up of a glass tube with a small but uniform bore, a reservoir, or bulb, at the bottom and a sealed end at the top. The bulb and part of the tube are filled with mercury.
When the temperature being measured goes up, the volume in the mercury increases more than the capacity of the glass bulb. Therefore, the mercury rises in the tube. The temperature of the substance is that which the top point of the mercury reaches on the scale marked on the outside of the thermometer.
A deformation type thermometer operates on the principle that liquids increase in volume and solids increase in length as their temperature rise. The most common thermometer of this type is called the "bimetallic" thermometer.
A bimetallic thermometer is made up of two strips of different metals, such as iron and brass, which are firmly fastened together along their entire length.
An increase in temperature will cause brass to expand about twice as much as iron. The bar made up of these two strips will bend when their temperature is changed, because of the unequal changes in length.
If one end of the bar is securely fastened, the motion of the other end of the bar may be magnified by levers. This motion may be directed to a pointer. If the pointer is a pen, a record can be made of the temperature and its changes on paper moved by a revolving drum..