234 



Our Surroundings 



Transformer 



Microphone 



Dynamo 



AN EARLY BROADCASTING SET 



will make a shadow picture upon 

 the plate. The flesh will be faintly 

 outlined but the 'bones will show 

 a strong shadow. This picture is 

 then developed like any photo- 

 graphic plate. 



The value of the X-ray to man 

 is very great. With its aid sur- 

 geons can determine the extent of 

 any injury to bones and can locate 

 foreign objects that become lodged 

 in the body. Physicians also find 

 the use of these rays valuable in 

 the diagnosis of certain diseases 

 involving growths on the lungs and 

 other tissues of the body, for such 

 growths cast a darker shadow than 

 flesh. 



Radio. Another form of 

 radiant energy is illustrated in 

 radio, or wireless communication. 

 This is another example of the 

 transformation of energy. Radio 

 was made possible by a discovery 

 made by Heinrich Hertz, a Ger- 

 man scientist, in 1888. He dis- 

 covered that certain electrical dis- 

 charges through the air, known as 

 sparks, are each made up of thou- 

 sands of to-and-fro vibrations per 

 second, which cause ether waves 

 that radiate in all directions. In 

 honor of the discoverer these 

 waves are called Hertzian waves. 

 Their to-and-fro vibrations are 

 called oscillations. By observing 

 the pendulum of a clock in action 



