IV PREFACE. 



Children should learn the appearance and properties of every 

 common metal ; for there is no person to whom the knowledge 

 would, in any part of life, be useless. 



There are seventeen, perhaps nineteen, elementary substances 

 in all, which enter into the composition of plants and animals. 

 These, combined, form the numberless objects which are exhibited 

 by the vegetable and animal kingdom, and children should be 

 taught the nature, properties and uses of these elements. 



We live surrounded by the air, which is composed of two invis 

 ible gases, oxygen and nitrogen, both essential to the life of 

 every animal and of every plant. Children do not see air, nor 

 oxygen, nor nitrogen ; but they are just as able to understand 

 this mixture, both ingredients of which are invisible, as they are 

 to understand, what they often see, that salt becomes invisible in 

 water, and steam and smoke in the air. Show them a piece 

 of clean, bright iron, and another of rusty iron, and explain to 

 them that it is the oxygen of the air which has combined with 

 the iron, and converted it into rust or dirt, and they will be 

 prepared to comprehend all that you have to teach them about 

 the combinations of oxygen and other elements with each other. 



Plants feed on carbonic acid and ammonia. When children 

 understand what these are, there is nothing you can tell them more 

 curious and wonderful than the fact, that the wind which blows 

 from the habitations of men carries with it these gases, offensive 

 and poisonous to animals, but that rain dissolves and brings them 

 down to the roots, and that plants live upon them. 



All these facts are perfectly intelligible to children at an age 

 as early as that at which they are capable of learning grammar 

 and geography. Every fact to be presented is a simple fact. 

 There is scarcely one in natural history, or in the sciences on 



