xi LIGHT 163 



through. Move one of the cards aside, and notice that you 

 can no longer see the light. It must be remembered that 

 what we have said about light applies equally to all other 

 kinds of radiation. 



EXPT. 159. Place a stick vertically between the wall and a 

 long thin luminous gas flame. Notice that the shadow of the 

 stick is sharply denned. 



EXPT. 160. Construct a pin-hole camera as follows : Make 

 two paste-board tubes, by rolling pasted paper on a wooden 

 cylinder, so that one fits 

 inside the other. For the 

 wider tube previously 

 cover the cylinder with 

 dry paper. Cover one 

 end of the narrower tube Fl - 72. A Pin-hole Camera. 



with tissue paper and 



thrust this end into the wider tube. Line with black paper. 

 Notice pictures on the tissue paper. Reason out how they 

 are formed. Many toy-shops sell cheap pin-hole cameras, 

 which may be used instead of constructing one from tubes. 



EXPT. 161. Cover a lantern cap with tinfoil, remove the 

 condensing lens, and place the cap on. Make pin-holes in 

 the cap. For every pin-hole there is an image formed on the 

 screen. Make the pin-holes more and more numerous, and 

 near together, till the images overlap and become confused. 

 At last diffused light is produced, which is an overlapping of 

 images. 



Reflection of Light. When any wave is said to be reflected, 

 it is understood that it comes into contact with the surface of 

 some body, and is thrown back from that surface, and travels in 

 a direction opposed to that in which it was originally moving. 

 This may happen in two ways, either regularly or irregularly. 

 In the first case it is turned back according to fixed rules, while 

 in the second there is no uniformity about the reflection. The 

 page on which this is printed appears to be white because, owing 

 to -the roughness of the paper, of the irregular reflection of the 

 light which falls upon it. Or, if we powder a sheet of glass, 

 the powder seems to be white for a similar reason ; there are 

 many surfaces formed from which irregular reflection takes 

 place. 



Regular Reflection of Light. Light is regularly reflected 



M2 



