Heat and Temperature. 25 



up vibrations within the molecules themselves, which in 

 time may become so intense as to overcome the force by 

 which the components are bound together and the molecule 

 is thrown into parts, setting them free so that when their 

 motion slows down they may join in new combinations. 

 It is much as if some giant power were to seize upon a steel 

 chain, throwing it into such intense vibrations that its sev- 

 eral links are broken. 



31. Nature of Heat and Cold. When a body becomes 

 warm the rate of vibration of the molecules which compose 

 it is increased and the path through which they move 

 becomes longer. If the body becomes cold the rate of 

 movement of the molecules becomes less rapid and the dis- 

 tance through which they move less. The higher the rate 

 of molecular motion within a given body the warmer that 

 body is and vice versa. If the molecular motion of a body 

 could be completely brought to rest its temperature would 

 be absolute zero. Under this condition it is supposed that 

 any body would have its smallest volume; and all liquids 

 and gases would become solid. 



32. Temperature. When the temperature of a body is 

 given it is intended to state the degree of molecular vibra- 

 tion within it. The temperature at which a Fahrenheit 

 thermometer marks zero is not that of no molecular motion 

 but simply 32 degrees of that scale slower than the rate at 

 which pure water becomes a solid ; while zero indicated by 

 a Centigrade thermometer is the rate of molecular motion 

 which permits water to become solid and is a temperature 

 273 degrees above what is assumed to be absolute zero or 

 the condition of absolute rest. 



33. How Temperature is Measured. It is a general law 

 that those substances which may exist as solids, as liquids 

 or as gases, as is the case with water, which WP know as ice, 

 water and steam, or invisible vapor, change from the solid 

 to the liquid form and from the liquid to the gaseous form 

 when the rate of molecular motion has reached a certain 



