THE LUSTER ITS CAUSE EXPLAINED 177 



Fig. 43. This illustrates the similarity in the structure of the 



the pearl and the onion, and shows the manner in which 



rays of light are inflected from the strata of 



the pearl, thus causing the luster. 



they will be divided. This peculiar inflection of .the rays 

 of light from the different strata of the pearl is another 

 fine example of the phenomenon of interference. 



Some pearls are so extremely translucent the light can 

 almost pass through them, and these, of course, present 

 the very finest degree of luster. 



The perfectly round pearls have the Ivst luster on ac- 

 count of their more perfect arrangement of strata for 

 producing these phenomena, although the other forms are 

 capable of inflecting the rays of light and have beautiful 

 radiant lusters. 



The soft velvety skin of the pearl increases and en- 

 riches its delicate sheen. 



