A collection of 109 questions asked by children forms the foundation on which this book is built. The questions collected were asked by several hundred children in the upper elementary grades, over a period of a year and a half. They are intended to give the student very definite training in explaining the common things around him or her. They are intended also to make science accessible to readers of all ages. The book includes all the questions and answers that students need to know about gravitation, molecular attraction, conservation of energy, heat, light, sound, magnetism, electricity, mingling of molecules, chemical change and energy, and solution and chemical action.