PREFACE 



A COLLECTION of about 2000 questions asked by chil- 

 dren forms the foundation on which this book is built. 

 Rather than decide what it is that children ought to know, 

 or what knowledge could best be fitted into some educa- 

 tional theory, an attempt was made to find out what 

 children want to know. The obvious way to discover 

 this was to let them ask questions. 



The questions collected were asked by several hundred 

 children in the upper elementary grades, over a period 

 of a year and a half. They were then sorted and classified 

 according to the scientific principles needed in order to 

 answer them. These principles constitute the skeleton 

 of this course. The questions gave a very fair indica- 

 tion of the parts of science in which children are most 

 interested. Physics, in simple, qualitative form, not 

 mathematical physics, of course, comes first ; astron- 

 omy next; chemistry, geology, and certain forms of 

 physical geography (weather, volcanoes, earthquakes, 

 etc.) come third ; biology, with physiology and hygiene, 

 is a close fourth ; and nature study, in the ordinary 

 school sense of the term, comes in hardly at all. 



The chapter headings of this book might indicate that 

 the course has to do with physics and chemistry only. 

 This is because general physical and chemical principles 

 form a unifying and inclusive matrix for the mass of ap- 

 plications. But the examples and descriptions through- 

 out the book include physical geography and the life 

 sciences. Descriptive astronomy and geology have, 

 however, been omitted. These two subjects can be best 

 grasped in a reading course and field trips, and they have 

 been incorporated in separate books. 



