330 



GENERAL SCIENCE 



The use of a mirror to reflect light so as to produce images is 

 very important in the submarine. The periscope is made up of a 



round barrel containing 

 mirrors which reflect the 

 light down into the in- 

 terior of the submarine, 

 thus giving a picture of 

 the surroundings when the 

 top of the periscope is 

 above the water. 



Mirrors are also used 

 for signal work in an in- 

 strument called the helio- 

 graph. 



With a mirror try to 

 reflect rays of sunlight to 

 different parts of the room. 

 Law of Reflection. A 

 person standing directly 

 in front of a mirror sees 

 his own image, but if he 

 stands at the side of the 

 mirror he is unable to see 

 his own image, although 

 it can be seen plainly by 

 a second person standing 

 on the opposite side of the 

 mirror. The reason for 

 this is easily seen when 

 we know that light is re- 

 flected at the same angle 

 at which it hits the mirror. 

 This is called the law of 

 reflection, and the angle 

 formed by the ray coming 



to the mirror is called the angle of incidence. The angle formed 

 by the ray which is reflected from the mirror is called the angle 



FIG. 201. This picture of the conning-tower and 

 apparatus on deck shows the massiveness of 

 the most modern kind of submarine. New and 

 larger types are constantly being built. 



Courtesy Child's Book of Knowledge. 



