SCIENCE OF COMMON THINGS. 261 



Opaque and transparent bodies. Absorption of light. 



Those which do not irvterrupt the , passage of light, 

 or which admit of other bodies being seen through 

 them. 



1606 When is a body said io be opaque ? 



When it entirely prevents the passage of light. 



1607 Is there any body perfectly transparent f 



No ; some light is evidently lost in passing even 

 through space, and still more in traversing our atmo- 

 sphere. 



160S Row much of Vie sun's light is supposed to be intercepted by the 



atmosphere ? 



It has been calculated that the atmosphere, when the 

 rajs of the sun ^>ass perpendicularly through it, inter- 

 cepts from one-fifth to one-fourth of their light; but 

 when the sun is near the horizon, and the mass of air 

 through which the solar rays pass is consequently 

 vastly increased in thickness, only one two hundred and 

 twelfth part of their light can reach the surface of the 

 earth. 



1S00 Why is charcoal black f 



Because it absorbs all the light which falls upon it, 

 and reflects none. 



1*700 What becomes of the light which is absorbed? 



This question cannot be satisfactorily answered. In 

 all probability it is permanently retained within the 

 substance of the absorbing body. 



1*7O1 To what depth is light supposed to penetrate tJie ocean f 



It is calculated that sea water loses all its transpa- 

 rency at the depth of seven hundred and thirty feet ; 

 but a dim twilight must prevail much deeper in the 

 ocean. 



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