MECHANICAL POWEE CHANGED TO HEAT. 391 



on its buckets. Thus to raise a hammer wefghing ten pounds 

 to the height of one foot requires at least the fall of ten pounds 

 weight of water from a height of a foot. It was then, properly 

 speaking, this weight of falling water which produced the 

 heat through means of the hammer. By simply altering the 

 arrangement of the machinery, the same force would have 

 caused a mill-stone to revolve with great rapidity on its axis, 

 or raised by friction two iron disks to a red heat. 



From experiments instituted to elucidate this point, it has 

 been established that 13,500 blows of a hammer, weighing 10 

 pounds, falling on a bar of iron from a height of one foot, pro- 

 duce an amount of heat sufficient to raise one pound of water 

 from the freezing point to that of ebullition. This fact may 

 be represented in another way by saying, that 1,350 cwts. of 

 water, falling from a height of one foot, will raise the temper- 

 ature of 1 Ib. of water from freezing to the boiling point ; or 

 1,350 Ibs. of water falling from the same height will raise one 

 pound of water one degree in temperature, or in other words, 

 that this amount of heat corresponds to a working power, 

 capable of elevating 13^ cwt. to the height of one foot. 



Wherever motion is lost in a machine by friction or by 

 concussion, there is always produced a corresponding amount 

 of heat. When, on the other hand, a certain quantity of 

 work is performed by heat, there disappears, with the me- 

 chanical effect obtained, a certain amount of heat, which is 

 expressed by saying that the heat lost by one pound of water 

 in falling one degree in temperature, is equal to the elevation 

 of 13 J cwt. to the height of one foot. This quantity of heat 

 becomes then the equivalent or value of the working power 

 expressed by the above numbers. 



This constant relation between heat and mechanical move- 

 ment has been confirmed in the most varied manner. A rod 

 of metal is extended by a weight, and on its removal resumes 

 its original length, provided certain limits be not exceeded. 

 The same effect is produced by heat ; and it is evident that 



