14 CHEMISTRY AN ADDITIONAL SENSE. 



he has to do, provided he also has practical skill, is 

 obviously in a much better position than the one who 

 knows nothing of them, and scorns the very idea of 

 learning anything from books. The former shapes his 

 course from certainties, from actual reasoning based 

 on his own knowledge; the latter does any particular 

 thing only because he has seen it done before, or per- 

 haps because some other person recommends it. 



Carbon is the only one of these four substances that 

 is visible or tangible to our unaided senses, but we see 

 that there are means of recognizing the others; that 

 we are able to perceive their properties, and even to 

 reason upon their various uses, with no less certainty 

 than if we were able to grasp them in our hands and 

 hold them up for inspection. Chemistry may thus be 

 considered an additional sense. 



