306 TEMPERATURE. 



gives rise to the well known sensations of warmth 

 and cold. By means of these effects upon the animal 

 body it is generally recognized. Being a form of energy, 

 it is a measurable quantity but not a material substance. 



474. What is Temperature tThe tempera- 

 ture of a body is Us state considered with refer- 

 ence to its ability to communicate heat to other 

 bodies. It is a term used to indicate how hot or cold 

 a body is. When a body receives heat its temperature 

 generally rises, but sometimes a change of condition 

 ( 53) results instead. When a body gives up heat, its 

 temperature falls or its physical condition changes. 



475. An Unsafe Standard. When we put a very warm 

 hand into water at the ordinary temperature, we say that the water 

 is cold. If another person should put a very cold hand into the 

 same water he would say that the water is warm. If a person place 

 one hand in water freezing cold and the other hand in water as hot 

 as he can endure, and, after holding them there some time, plunge 

 them simultaneously into water at the ordinary temperature, the 

 hand from the cold water feels warm while the hand from the hot 

 water feels cold. These experiments show that bodily sensations 

 cannot be trusted to measure this form of energy that we call heat. 



476. Thermometers. An instrument for 

 measuring temperature is called a thermometer. 

 The mercury thermometer is the most common. Its ac- 

 tion depends upon the facts that heat expands mercury 

 more than it does glass, and that when two bodies of dif- 

 ferent temperatures are brought into contact, the warmer 

 one will give heat to the colder one until they have a com- 

 mon temperature. 



477. Graduation of Thermometers. Ther- 

 mometers are graduated in different ways, but in all cases 

 there are two fixed points, viz., the freezing and the boiling 



