8 THE riuxci! Li:s of agrtcultihe. 



The whole number of elementary suhstances nt present 

 known is from sixty-live to seventy. Some of them, how- 

 ever, are very rare. 



Only fourteen elements are generally found in soil, 

 ])lants, and animals. Knowledge of these is of impor- 

 tance in the study of agriculture. 



They are as follows : — 



These names are used so often that, for convenience, 

 they are abbreviated, each being represented by one or 

 two letters. The abbreviations are axWed' symhols. The 

 symbols for potassium, sodium, and iron are taken from 

 the ancient and foreign names of those sulistances. 



Atoms. — All matter is composed of minute particles 

 called atom^. These are so small that they have never 

 been seen. We cannot even imagine the size of them. 

 Millions of atoms might I'cst upon the point of a pin. 



The belief tliat they exist is embodied in what is called 

 the atomic theori/. This theoiy is believed to be true, 

 because all known facts are consistent with it. All the 

 facts in nature with which we are acquainted, and the 

 results of all experiments that have ever been tried, are 

 just what they would be if the theory were true. The 

 fact that atoms cannot be seen is no reason for doubting 

 their existence. We are limited in our power to see 

 and nndei'stand. As we are unable to comprehend tlie 

 distance to tlic sun, and the immensity of spnce, so, on 



