194 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



Apparatus for the Polarization of Light. The phenomena 

 produced by the polarization of light are among the most 

 splendid and singular in the whole range of physical science. 

 Common light consists of undulations, in which the vibra- 

 tions of each particle are in the plane perpendicular to the 

 wave's motion. The polarization of light is the resolution 

 of each vibration into two ; one parallel to a given plane 

 passing through the direction of the wave's motion, and 

 the other perpendicular to that plane, which become in cer- 

 tain cases the origin of waves that travel in different direc- 

 tions. When we are able to separate one of these from the 

 other, we say that the light is polarized. Or, in simpler 

 language, we would say, when the light of the sun is re- 

 flected from certain bodies at particular angles, according to 

 the nature of those bodies (as glass at an angle of 56 45'), 

 or by transmission through a plate of tourmaline, and also 

 through doubly refractive crystals (as carbonate of lime), 

 and these bodies are turned round, the light becomes in a 

 measure decomposed, one side of the ray presenting an ap- 

 pearance and properties different from the other ; these two 

 contrary sides are said to be the poles of the ray, and the 

 whole light becomes polarized light. 



Prism for Double Refraction. (Figs. 7 10 and 711.) The 

 best substance for showing the phenomenon of double re- 

 fraction, is that form of carbonate of lime, called Iceland 

 Spar. This substance exhibits the double refraction in 

 great perfection. The rhomboidal form is the most con- 

 Fig. 710. Fig. 711. 



venient. Let a black line be drawn on a piece of paper, 

 and let a rhomb of this spar be laid upon it ; then, on look- 

 through the upper face of the spar, down on the paper, two 

 lines will be seen, and any object viewed at a distance 



