60 THE STORY-BOOK OF SCIENCE 



change to earthy matter, as does the blade of a 

 knife hurled in the ground." 



"JMv hrother seems to reason correctly; I agree 

 with him," said Claire. 



"And gold?" Uncle Paul asked her. 



"It is different with gold," she replied. "As that 

 metal never rusts, is not changed by time, air, and 

 dampness, it must be pure." 



"Kxactly so. In the rocks where it is dissemi- 

 nated in small scales, gold is as brilliant as in jewel- 

 ers' boxes. Claire's earrings have not more luster 

 than the particles set by nature in the rock. On the 

 contrary, what a pitiful appearance iron makes 

 when it is found! It is an earthy crust, a reddish 

 stone, in which only after long research can one sus- 

 pect the presence of a metal; it is, in fact, rust, 

 mixed more or less with other substances. And 

 then, it is not enough to perceive that this rusty 

 stone contains a metal; a way must still be found 

 to decompose the ore and bring the iron back to 

 its metallic state. How many efforts were neces- 

 sary to attain this result, one of the most difficult 

 to achieve! How many fruitless attempts, how 

 many painful trials ! Iron, then, was the last to be- 

 come of use to us, long after gold and other metals, 

 like copper and silver, which are sometimes, but 

 not always, found pure. That most useful of 

 metals was the last ; but with it an immense advance 

 was made in human industry. From the moment 

 man was in possession of iron, he found himself 

 master of the earth. 



"At tlie head of substances that resist shock, iron 



