THE EEASON WHY. 129 



"A man that is called Jesus made clay, and anointed mine eyes, and said unto 



me, Go to the pool of Siloam, and wash : and I went and washed, 



and I received sight." JOHN ix. 



illuminate every atom of the permeated substance, and by surround- 

 ing it with a prismatic clothing, to afford an illustration of its 

 molecular arrangement. 



551. Why are two persons able to see each other ? 

 Because rays of light flow from their bodies to each other's eyes, 



and convey an impression of their respective conditions. 



In some popular works that have come under our notice, we find that the 

 student is told that "we cannot absolutely see each other we only see the rays 

 of light reflected from each other" The statement is erroneous as expressed. 

 We do riot see the rays of light, for if we did so, the effect of vision would be 

 destroyed, and all bodies would appear to be in a state of incandesence, or of 

 phosphoresence. Rays of light, which are in themselves in-visible, radiate from 

 the objects we look upon, enter the pupil of the eye, and impress the seat of 

 vision in a manner which conveys to the mind a knowledge of the form, colour, 

 and relative size and position of the figure we look upon. If this is not seeing 

 the object what is? It would be just as reasonable to say, that we cannot 

 hear a person speak that we only hear the vibrations of the air. But as the 

 vibrations are imparted to the air by the organs of voice of the speaker, 

 as he sets the air in motion, and makes the air his messenger to us, we cer- 

 tainly hear him, and can dispense with any logical myths that confound the 

 understanding, and contribute to no good result. 



552. What is actinism ? 



Actinism is the chemical property of light. 

 Actinism ray power. 



553. Why does silver tarnish when exposed to light? 

 Because of the actinic, or chemical power of the rays of the sun. 



554. Why do some colours fade, and others darken, when 

 exposed to the sun ? 



Because of the chemical power of the sun's rays. 



555. Why can pictures lie taken ty the sun's rays ? 

 Because of the actinic powers that accompany the solar light. 



556. What is the particular chemical effect of light 

 exhibited in the production of photographic pictures ? 



Simply the darkening of preparations of silver, by tJie aclinic 



rays. 



557. Why are photographic studios usually glazed with 

 Hue glass ? 



6* 



