Lesson X. 





i.M 



/'. Light being transmitted m straight 

 lines, it follows that a dark body -\ 



of li L 'ht must throw a sh-idow, 

 because the light does not pass through ; 

 rt F will illustrate this in a familiar 



Fig. 30. 



way. [Experiment 17.] Place a lighted 

 candle in the centre of a small table (as in , 

 / i , then tie a thread to the stalk of 



an apple, and hold it high above the lijzht 



.nother thread to j 



another apple, and I will hold it nearly on 

 a level with the table (as B Fig 30); now 

 you observe that the half of each apple is 



light, and the other part dark, the lighted 

 part being nearer to the candle, and the 

 dark part farther from it. > 

 no actual shadow cast from the apples 

 held in the hands; but if you look at tin- 

 stand of the table you will observe that 

 there are shadows (c & D) thrown from 

 it ; this is because the natural light strikes 

 thi> other side, and therefore the part 

 beyond it forms the limits of th<- shadow. 

 In this manner vre can understand how 

 the shadow of a body exposed to the 

 sun's light is sharply defined close Miind 

 it, while at a greater distance it becomes 

 undefined. 



IIONS ON LESSON 1\ 



1 . Describe light. 



2. How is light produced? 



i >w is light transmitted? and what 

 is meant by a medium ? 



4. Describe the difference between 

 opacity, transparency, and transit; 

 and also what is meant by diaphonous. 



:> What takes place when a ray of 

 light is interrupted in its course? 



f,. How fast does light travel? 



7. Kxplain how shadows are formed. 



V 



1 ii K intensity of light diminishes in proportion as the squares of tl 

 increase. This is a known fact of much importance in optics, and should therefore be 



ring more fully into |] . it will be well to explain some of the 



.n common use. il is a slender portion of rays, or a small bundle of 



a beam is a large bundle of pencils. Rays are said to ./ i they 



separate from each other as t i. trom the luminous {mint; and 00) 



proach closer to each other, until they meet in a. point. All rays are originally 

 made to converge by the aid of some substance having a 

 e or refractive power. The M >/* is the point from which rays diverp 

 they conv< ifl the point to which parallel rays arc 



made to con. llection -r rei'ra. re those which e-ntimu 



n direct course side hy side, at the same dist:i ach other, thus Z 



no sur ngth ^^ 



distance between the focus and (lie r< tl< cting or refracting 



body. 



Reflected ray* are thrown back ft which they fall. 



ray* are not thrown back, ' m in an alter. 



