38 MOTIVE POWER OF HEAT. 



man has thus far employed but a small portion. 

 Even earthquakes and volcanic eruptions are the 

 result of heat. 



From this immense reservoir we may draw the 

 moving force necessary for our purposes. Nature, 

 in providing us with combustibles on all sides, 

 has given us the power to produce, at all times and 

 in all places, heat and the impelling power which 

 is the result of it. To develop this power, to 

 appropriate it to our uses, is the object of heat- 

 engines. 



The study of these engines is of the greatest 

 interest, their importance is enormous, their use 

 is continually increasing, and they seem destined 

 to produce a great revolution in the civilized world. 



Already the steam-engine works our mines, im- 

 pels our ships, excavates our ports and our rivers, 

 forges iron, fashions wood, grinds grains, spins 

 and weaves our cloths, transports the heaviest 

 burdens, etc. It appears that it must some day 

 serve as a universal motor, and be substituted for 

 animal power, waterfalls, and air currents. 



Over the first of these motors it has the advan- 

 tage of economy, over the two others the inestima- 

 ble advantage that it can be used at all times and 

 places without interruption. 



If, some day, the steam-engine shall be so per- 



