28 NATURE-STUDY 



They can easily see that the fox is like the dog, both in struct- 

 ure and in habits, and they will naturally group them to- 

 gether. But have them also note the essential differences 

 that make one animal a dog and the other a fox. The more 

 common type, the dog, should be studied first. Then, in 

 studying the fox, compare his head with that of the dog; 

 then the teeth, the feet, and the habits, as these points are 

 brought out in the developed description of the fox. Or 

 wait until the fox description is finished and then compare. 

 Sometimes a superficial resemblance of two objects resolves 

 itself after comparison into wide differences. For instance, 

 most people call the chimney-swift a swallow. But a careful 

 comparison shows that the birds belong to different groups. 

 The comparison of physical phenomena, such as conduction 

 and convection, is good practice and leads to clearer reason- 

 ing. Comparison is. a necessary step where classification is 

 desired. , 



Sometimes all the facts developed in a nature lesson are 

 considered together, and some generalization is derived from 

 them. Comparison of several objects or facts leads to classi- 

 fication, a kind of generalization. But sometimes a general 

 principle is involved in a number of illustrations or experi- 

 ments, and this the children are to think out. Thus, a 

 number of experiments in heat may all lead to the conclusion 

 that heat causes expansion. 



When such generalizations have been made, the pupils 

 should be required to think of applications of the principle 

 in new cases. Thus, after deriving the principle of expansion 

 by heat, let the pupils apply this principle to such cases as 

 the setting of wagon tires, the gap between the rails, the 

 thermometer, etc. This fixes the principle better in the 



