Lesson X. 







/'. Light being transmitted in straight light. and the other part dark, the lighted 

 ' follows that a dark body exposed part brine; nearer to the candle, and the 

 I of light must throw a shadow, ' dark pan farther from it. N 

 because the light does not pass through no actual shadow cast from the apples 

 I will illustrate this in a familiar held in the hands; but if you look at the 



| stand of the table you will observe that 

 there are shadows (c & D) thrown from 



I because the natural light st: 

 the other side, and therefore the. part 



i it forms the limits of t 

 In tliis manner we can understand how 

 :dow of a body exposed t<> the 

 sun's light is sharply defined 

 it, while at a greater distance it V 

 undefined. 



,;.\L QUESTIONS ON LESSON I\ 



1 . Describe light. 



-2. How is light produced? 



, .\v 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 Mkes place when a ray of 

 light is interrupted in its con: 

 : ist does light tra . 



7. Explain how shadows are formed. 



Fig. SO. 



way. [Experiment 17.] Place a lighted 

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

 -n tie a thread to the stalk of 

 an apple, and hold it high above the light 



nother thr. 



another apple, and I will hold it nearly on 



with the table (as B Fig 30); now 



-ervc that the half of each apple is 



I8OV v 



nsity of light diminishes in proportion as the squares of the d.< 

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

 red. 



ring more fully into the science, it will be well to explain some <>f thv 

 ;n common use. Thus a pencil is a slender portion of rays, or a small bundle of 



a beam is a large bundle of pencils. Rays are said to diverts 

 separate from each other as 1 1 from the luminous point; a 



proach closer t> each other. umiJ ; >int All rays ai 



v are made to converge by the aid of some substance having u 

 ;ve or refractive power. The /<>.< is the point from which rays diverp 



they conv. ./i/ _/.Viw is the point to which parallel rays are 



made to converge by reflection or refra< re those wh 



n direct coarse side by side, at the same distance from each other, thus 

 no su< .illy exist The focal ngth ^A 



distance between the focus and tl : g or refracting ^^ body. 



Reflected roy re thrown back !" which they fall. 1 



ray* are not thrown back, bat pass through th> indium in an alien 

 [See Question 110.] 



