no NATURE STUDY BY GRADES 



What happens if too much light enters the eye ? Why do 

 we have to use a smoked glass to look at the sun? What 

 happens when little or no light enters the eye? Consider 

 the disadvantages of the blind. Why can an owl or a horse 

 or a cat see at night better than we can ? This window can 

 be made larger to admit more light from objects. Why are 

 the fishes and crawfishes in the Mammoth Cave blind ? If 

 they had eyes, of what use would they be ? 



Look at a cat's eyes. Notice how long and narrow the 

 pupil is : when it opens at night or in the dark, it is much 

 larger than the pupil of a person's eye. 



What care should be taken of the eyes ? 



LESSON XXXIII 

 EVAPORATION 



What becomes of the water when the teakettle boils dry ? 

 when wet clothes are hung out on the line to dry ? Does all 

 the rain after a shower soak into the ground? Refer to 

 many familiar examples of water disappearing in this way. 

 Perform a few simple experiments to illustrate evaporation. 



Do other liquids evaporate? Show by experiment that 

 alcohol, turpentine, gasoline, ammonia, chloroform, and 

 many other liquids pass readily into vapor, and that glycer- 

 ine, olive oil, pitch, tar, and perhaps other liquids evaporate 

 very slowly, if at all. Note that the rate of evaporation 

 differs greatly for different liquids. 



What is steam ? What are clouds ? How are they made ? 

 Mention many ways in which evaporation is a blessing. 

 What will hasten evaporation ? How can we hinder or pre- 

 vent evaporation ? Give illustration. 



