18 



CHEMISTRY. 



resist the tendency of its body to persevere in the 

 rapid motion it had acquired, and is therefore ur- 

 ged many yards before it is able to check its speed 

 and return to the pursuit. In the mean time, the 

 hare is gaining ground, and thus, though much less 

 fleet, often escapes. The fox* also is known to 

 practise the same artifice. 



CHAPTER II. 



CHEMICAL CONSTITUTION OF THE EARTH'S SURFACE. 



Definition. — Four Elements according to the Ancients. — Chief 

 Chemical Elements which enter into the Earth's Crust : Ox- 

 ygen, Hydrogen, Nitrogen, Carbon, Sulphur, Chlorine, Fluo- 

 rine, Phosphorus. — Metallic Bases of the Alkalies and Earths: 

 Silica, Alumina, Potassium, Sodium, Magnesium, Calcium. — 

 Imponderable Agents : Heat, Light, Electricity, Galvanism. — 

 Thermometer. — Affinity. — Cohesion. — Illustrations. — Com- 

 pound Elective Affinity. — Cases. 



Chemistry has been defined to be the science of 

 analysis and combination. It leads us to a knowl- 

 edge of what bodies are composed ; teaches us the 

 nature and properties of their several elements, un- 

 der what circumstances these elements unite, and 

 the result of such union. Of course, a knowledge 

 of this science is essential in ascertaining the na- 

 ture of the materials which enter into the constitu- 

 tion of our globe, as well as the laws which regu- 

 late their combination. 



The ancients believed that there were but four 

 elements : fire, water, air, and earth ; and, conse- 

 quently, that all bodies were formed by a union of 



* Dr. Lardner. 



