CHAPTEE II. 



TRANSFORMATIONS OF ENERGY. 



AS already stated, the energy of motion of a moving 

 body is due to its mass multiplied into the height 

 from which it must have fallen in order to acquire its 

 velocity.^ And also, its energy of motion is proportionate Energy of 

 to its mass multiplied into the square of its velocity. ™° ^°"' 

 Energy of motion is thus definitely measurable by 

 quantity. 



Heat is also definitely measurable by quantity. Equal and heat, 

 quantities of heat are those which equally increase the nleasur- 

 temperature of equal quantities of the same substance, able by 

 For instance : equal quantities of heat will raise the tern- Measure 

 perature of equal quantities of water by one degree of the °f ^*''^*- 

 thermometer. 



N"ow, it is found by experiment that eqtial quantities of 

 energy of viotion are capahle of transformation into equal 

 quantities of heat; and, conversely, equal quantities of 

 heat are capable of transformation into equal quantities of 

 energy of motion. This is called the law of the dynamical Dynamical 

 equivalent of heat. Its numerical statement is, that the of^eat^"^ 

 energy which is due to the descent of one pound of weight 

 of any substance whatever through 772 feet of height is 

 capable of transformation into so much heat as will raise 

 the temperature of one pound of water by 1° Fahr.^ This, 



' See page 20. 



- Tyudall on Heat as a Mode of Motion, p. 40. It would take a fall 

 through 1,390 feet to raise the temperature of a pound of water by 1° 

 Centigrade. 



