144 OF POLARIZED LIGHT. 



phenomena, have made it one of the most attractive 

 subjects of modern science. 



Ordinary light passes through transparent bodies 

 without producing any very striking effects in its pas- 

 sage; but this extraordinary beam of light has the 

 power of insinuating itself between the molecules of 

 bodies, and by illuminating them, and giving them every 

 variety of prismatic hue, of enabling the eye to detect 

 something of the structure of the mass. The chromatic 

 phenomena of polarized light are so striking, that no 

 description can convey an adequate idea of their cha- 

 racter. 



Spectra more beautiful and intense than the pris- 

 matic image, systems of rings far excelling those of 

 thin plates, and forms of the most symmetric order, are 

 constantly presenting themselves, as the polarized ray is 

 passed through various transparent substances; the 

 path of the ray indicating whether the crystal has been 

 formed round a single nucleus or axis, or whether it 

 has been produced by aggregation around two axes. The 

 coloured rings, and the dark or luminous crosses which 

 distinguish the path of the polarized ray, are respectively 

 due to different states of tension amongst the particles, 

 although those differences are so slight, that no other 

 means is of sufficient delicacy to detect the variation. 



The poetry which surrounds these, in every way, myste- 

 rious conditions of the solar beam, is such, that it is with 

 difficulty that imagination is restrained by the stern 

 features of truth. The uses of this peculiar property in 

 great natural phenomena are not yet made known to 

 us ; but, since we find on every side of us the natural 

 conditions for thus separating the beam of light, and 

 effecting its polarization, there must certainly be some 

 most important end for which it is designed by Him 

 who said, " Let there be Light." 



It must not be forgotten that we have at command 

 the means of showing that the chromatic phenomena of 



