40 NATURE-STUDY 



behave. If a thing always acts the same way under similar 

 conditions, we say so and tell how it acts. That is, we state 

 its law of action. Or, perhaps, the experiments bring out 

 certain qualities that the objects possess, and we may then 

 be able to classify the thing where it belongs. In general, 

 in an experiment, we look for certain phenomena or certain 

 quahties. These we make use of as the basis of our general- 

 izations, which may either be in the form of a law of action, or 

 a classification of facts or objects in their proper categories. 

 The experiment is the scientist's great test for truth. It is 

 the basis of practically all science. 



Many phenomena in nature-study demand experiments to 

 produce or to illustrate them. There are many simple ex- 

 periments that would dehght the children, give them useful 

 information, and at the same time afford excellent practice 

 in inductive reasoning. Touching a sensitive plant to see it 

 fold its leaflets, softening a bone in acid to show the need 

 of mineral matter to strengthen them, placing some leaves 

 under a bell-glass to see the evaporation of water from the 

 pores, testing a suspended magnet to see that it points north 

 and south, balancing a heavy weight by means of a small one 

 on a lever, rearing a caterpillar into a butterfly, — all these 

 and hosts of others are fit experiments for the grades. 



Consider the principle of expansion by heat. To show 

 this it is necessary to perform some simple experiments in 

 which this phenomenon appears. Perform the usual ex- 

 periments, such as the ball and ring experiment; heat some 

 water in a bottle with a narrow neck and note the rising of 

 the liquid on warming; repeat with the school-room ther- 

 mometer. Show also that a bottle filled with air expands 

 when heated. In ah these experiments the phenomenon of 



