PREFACE. 



THE design of the present volume is to furnish for the 

 use of schools and young persons, an elementary text-book 

 on the first principles of science. For this purpose, the 

 system of question and answer, which for certain classes 

 of pupils and for familiar instruction has proved emi- 

 nently popular, has been followed. The advantages of this 

 system are : first, that it affords a most simple and easy 

 method of communicating useful and practical informa- 

 tion : second, the question excites a feeling of curiosity in 

 the mind of the young student, which serves to fix the sub- 

 ject-matter more strongly in the memory : and thirdly, 

 the form of question and answer imparts truth to the mind, 

 in a logical sequence of cause and effect, and by showing 

 how consequents in sciences are deduced from antecedents, 

 unconsciously trains and familiarizes the pupil to think and 

 reason according to the true spirit of inductive philosophy. 



It is believed that the questions in the. present volume 

 are simple, practical, and expressed in the plainest language 

 that the subject allows. Engravings have also been used 

 to illustrate more clearly the most important topics treated 

 of. 



As this work has been designed exclusively as an elemen- 

 tary book, the more abstruse and difficult departments of 



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