1 92 Natural Theology. 



perature of the globe, remains unchanged for thou- 

 sands of years. But in the heat of .the furnace its 

 relative affinity is completely reversed, so that the 

 oxygen rushes from the iron ore to the heated car- 

 bon, leaving the iron in the metallic state for the 

 use of man. It is proper here to state, that this is 

 only one example of the change in the relative 

 strength of affinities by change of conditions ; taking 

 advantage of which, the chemist is able to unlock 

 every compound, and produce results entirely impos- 

 sible were the affinities of all substances increased 

 or diminished alike, by any change of condition. 

 The materials of gunpowder are ground and pressed 

 together, and yet the chemical affinities of the com- 

 pounds remain, at ordinary temperatures, unchanged. 

 The oxygen still clings to the potassium, holding 

 even the nitrogen with a firm grasp. But a single 

 spark of fire reverses these affinities in an instant, 

 so that there is an interchange of elements ; new 

 compounds are formed ; the solids change to gases 

 with terrible explosive power. 



When we see an element transforming the globe 

 from a ball of metal to the rocky crust of our earth, 

 forming its gems and soils, its oceans that beget 

 the springs, the rains, and dews ; when we see it 

 entering into the structure of .every living thing, 

 and essential to animal life for every moment ; when 

 we see it prepared in such quantity that when it 

 had formed all needed compounds, just enough was 

 left to carry on the processes of life ; when we see 

 its relation to light and heat, its passive and its 



