HEAT. 55 



"hand. "Water also bubbles and boils in natural pots, and steam 

 s out of natural funnels, with the force and noise of a 

 steamboat whistle. This all shows the result of chemical action, 

 by water, under the surface ; for we find that the action has 

 ceased in many spots, and every year it is travelling further 

 up the valley, and breaking out in nerw places. Mount St. 

 Helena which crowns the beautiful Napa Valley, and towers 

 over all the liills around, was once a volcano, but its action 

 has now ceased. Should not this lead us to believe that vol- 

 canoes also, are merely the result of chemical action ; else why 

 would they become extinct ? 



Let us now consider the second cause of heat in the process 

 of combustion, or heat from combustion. 



In the chapter on Matter, we stated that the mineral atoms 

 were combustible ; but minerals will not burn of themselves, for 

 in all continued action there must be a union of the two classes. 

 For example, sulphur will not burn while alone, but put some 

 portion on a piece of wood, the two substances will burn or re- 

 ciprocate together, and the consequence is we see the sulphur on 

 fire. Iron will not burn if alone, but when it is in fine 

 particles as filings, and separated, as in sprinkling them in 

 the atmosphere over a gas jet, they are combustible, and 

 when ignited burn more readily than gunpowder. "Wood 

 burns because there are mineral atoms in the composition and 

 formation of the woody fibre. "Wood is produced by a combi- 

 nation of vegetable and mineral atoms, through the agency of 

 water which comprises the element;- of both. 



This shows conclusively, tliat there is reciprocity and motion 

 in the process of chemical action, and of course, according to 

 the properties of the atoms the greater the motion, the greater 



