266 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



placed along the respective focal lines of two parabolic cylinders 

 made of sheet metal, as shown in Fig. 198 and the resonator was 

 arranged so that its spark gap was behind the mirror and thus 

 easily visible. 



Reflection of electric waves. When the oscillator and resona- 

 tor are arranged as shown in Fig. 198, a very distinct effect of 

 the resonator is produced when the oscilla- 

 tor is active, the waves from the oscillator 

 being concentrated upon the resonator by 

 the action of the two parabolic reflectors. 



When arranged as shown in Fig. 199, 

 AB being a plain sheet of metal, and the 

 angles </> being equal, a very distinct effect 

 on the resonator is produed. 



Refraction of electric waves. When the 

 oscillator and resonator are arranged as 

 shown in Fig. 200, in which PP repre- 

 sents a large prism, of asphaltum or paraffine, a very distinct 

 effect is produced upon the resonator. 



Polarization of electric waves. A frame strung with a grating 

 of fine metal wire acts as a good reflector for the waves from a 



Fig. 199. 



resonator 



Fig. 200. 



Hertz oscillator, when the wires of the grating are parallel to the 

 axis of the oscillator. When the wires of the grating are at right 

 angles to the axis of the oscillator, the waves pass through the 

 grating without perceptible diminution in intensity. Therefore 

 the waves from a Hertz oscillator are plane polarized. 



Stationary electric waves. If the plane waves from the oscil- 



