PLAN OF THE BOOK ix 



the body of the text. Instead of placing the exercises 

 in a separate chapter at the end of the book, they 

 occur in connection with the sections which they are 

 intended to illustrate. In this way the exercises be- 

 come part of the regular lessons, and the pupil learns 

 to associate them with the proper facts. 



While most of these exercises are so simple that 

 they can be shown with such appliances as are found 

 in the ordinary kitchen, they should be regarded as an 

 essential part of the text. The experiments should be 

 performed by the teacher before the class, and later 

 they may be repeated by the pupils at home or at 

 school. 



Reviews and Summaries. At the beginning of each 

 chapter that introduces a new and related subject there 

 is a paragraph reviewing briefly what has been taught 

 in the preceding chapters, and showing the relation 

 which this new chapter bears to the old and familiar. 

 This facilitates still more the organization of the facts 

 of this science and gives them their proper perspective. 

 It emphasizes, by embodying in the plan of the text, 

 that old and important pedagogical principle, " From 

 the known to the related unknown." Each chapter 

 closes with a brief summary of the main points to 

 be remembered. Such reviews and summaries are 

 absolutely essential to a mastery of the subject. A 

 very common mistake in teaching this subject is to 

 permit the related facts necessary to an intelligent 

 understanding of the new lesson or new topic to fade 

 out of the mind entirely. A systematic arrangement of 



