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 lime, 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. 
