LIQUID THERMOMETERS
A rough idea of the temperature of an object can be made out with our sense of touch, but it is not an object can be made out with our sense of touch, but it is not an accurate method of measuring temperature. A thermometer is a device used to measure the temperature of substances.
The first thermometer was constructed by Galileo in 1593. It was an air thermometer based on the thermal expansion of air. Later Newton developed a liquid thermometer and suggested the need for fixed points. Gabriel Fahrenheit developed a mercury thermometer in1720 while Anders Celsius constructed a mercury-in-glass thermometer in1742.
A thermometer works on the principle that substances expand on heating and contract on cooling.
Mercury or alcohol is used as thermometric liquids. These liquids expand uniformly when they are heated. For measuring low temperature alcohol is used, as mercury freezes at -39oC.
The thermometer consists of a thick glass tube of uniform bore. At one end of the tube, is a small narrow bulb which contains mercury. The air from the glass tube is completely removed and the other end is sealed.
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