MECHANISM OF NATURE 



But light penetrates some substances and not 

 others, or rather, different substances permit the 

 light to pass through in a different degree of per- 

 fection. 



And the more freely a substance permits the 

 passage of light, the less the substance is affected 

 by the light. 



There are few known solids which are perfectly 

 transparent, or what is called perfect, but liquids 

 are far more transparent than the same substance 

 in a solid state, and nearly all gases are transpar- 

 ent. Again, many solids that do not seem to be 

 transparent in the slightest degree, under ordi- 

 nary conditions, will become to some degree trans- 

 parent when they are worked down to a very thin 

 sheet. 



It seems then as if the property of transparency 

 were a result of the cellular construction of a sub- 

 stance, the light penetrating between the particles 

 more or less freely, according to the size of the 

 interstices and their continuations in straight lines. 



The particles of a gas are clear apart from one 

 another, and therefore Primary Spheres, in the 

 transmission of light, can pass freely between the 

 gas atoms or particles. 



Animal membrane, freed from fats and coarser 

 tissue, oiled paper and various other things of like 

 nature, while permitting the light to pass, do not 

 permit us to see things on the other side of them. 

 Yet a window of oiled paper will give light enough 

 to read by. 



206 



