TO THE TEACHER 



Do not test the children on the narrative description 

 which introduces most sections, nor require them to re- 

 cite on it. It is there merely to arouse their interest, 

 and that is likely to be checked if they think it is a lesson 

 to be learned. It is not at all necessary for them to 

 know everything in the introductory parts of each sec- 

 tion. If the children are interested, they will remember 

 what is valuable to them ; if they are not, do not pro- 

 long the agony. The questions which accompany and 

 follow the experiments, the applications or required ex- 

 planations at the ends of the sections, and the extensive 

 inference exercises, form an ample test of the child's grasp 

 of the principles under discussion. 



It is not necessary to have the children write up their 

 experiments. The experiments are a means to an end. 

 The end is the application of the principles to everyday 

 facts. If the children can make these applications, it 

 does not matter how much of the actual experiments 

 they remember. 



If possible, the experiments should be done by the 

 pupils individually or in couples, in a school laboratory. 

 Where this cannot be done, almost all the experiments 

 can be demonstrated from the teacher's desk if electricity, 

 water, and gas are to be had. Alcohol lamps can be sub- 

 stituted for gas, but they are less satisfactory. 



It is a good plan to have pupils report additional exem- 

 plifications of each principle from their home or play life, 

 and in a quick oral review to let the rest of the class name 

 the principles back of each example. 



This course is so arranged that it can be used accord- 

 ing to the regular class system of instruction, or according 



ix 



