Management of Light in Illumination. 105 



the light of the sun is to that of the full moon, at the 

 surface of the earth, as three htmdred thousand to one. 



But notwithstanding this astonishing power of ac- 

 commodation possessed by the organ of sight, yet, 

 when the eye passes suddenly from a strong light to 

 one much more feeble, and vice versa, nothing can 

 be distinctly seen for some moments. It is true that 

 the eye soon recovers from these momentary derange- 

 ments, and that habit has rendered them so familiar 

 to us that we seldom take any notice of them ; but it 

 is nevertheless most certain that they not only injure 

 the eye very much, and weaken it in such a manner as 

 to impair its faculties at a very early period of life, but 

 that they also render it impossible to see surrounding 

 objects so distinctly as they might be perceived, even 

 with much less light, were the illumination established 

 on better principles. 



The facility with which we see objects distinctly 

 depends much on their shadows. When the lights 

 and shades are simple and distinct, they are necessarily 

 well defined, and we see distinctly ; but when the light 

 arrives in several directions at the same time, the lu- 

 minous points of the object and its shadows are so 

 blended and confused that distinct vision is impossible, 

 whatever may be the intensity of the light present. 



A portrait painter never permits light to come into 

 his room but through one single window ; and those 

 who are desirous of having their apartments illumi- 

 nated at night in the pleasantest manner possible 

 must contrive to have all the light come from one 

 source. If every sudden change in the intensity of the 

 light that strikes the eyes is injurious to them, the 

 direct rays which proceed from the flames of lamps and. 



