^^ ON ILLUMINATION. 



It is well known tliat we can read printed characters of a 

 jnodenitc size, botli by the light of the full moon, and by that 

 of tlie sun at mid-day ; the intensity, however, of the lights 

 in the first case, is, to that in the second, as 1 to 300,000 ; 

 but when the eye passes rapidly from a strong light, to one 

 th&t is more feeble, or tice versa, wc c;iji distino;uish nothing 

 at first ; and, when these changes succeed each other rapidly, 

 they become extremely fatiguing to the eyes. 

 Cistinctnesc The facility with which we distinguish an enlightened ob- 



«l»>pends very j^^,^ depends on its shadow. When shadows are simple, they 

 simplicity of are necessarily well defined, and we see distinctly ;. but when 

 the shadows of ^j^g ]jg].j|. comes in several directions, several shadows are formed 

 of the same object, which are so blended together as to render 

 them confused and ill defined; and in that case we see indis- 

 tinctly, even in the midst of a great glare of light. Hence we 

 may conclude, that a considerable economy must result from 

 a judicious distribution of the light employed in lighting a 

 room. But this saving of expence, considerable as it would 

 "be, is however an objectiof much less Importance than the ad- 

 •vantage which must result in respect to the pleasantness of the 

 light, and the preservation of the eyes. 

 The turtful ef- If every sudden change In the intensity of the light that falls 

 recUMit of '' ^P^^" ^^^ ^y^s be hurtful to them, the direct rays coming from 

 lamps upon the flame of an Argand lamp must fatigue them very much, 

 theeje. ^^^ ^^.^^ deprive them of the faculty of distinguishing easily 



objects which are placed near that dazzling source of bright- 

 ness! It is impossible Indeed to view the flame of one of these 

 lamps near at hand without suffering excessive pain, and even 

 at a distance it is always hurtful and unpleasant to the eye. 

 It Is well known how much we are dazzled and almost blinded 

 on coming into a room lighted by several of these lamps, 

 burning whhout shades, and placed so low that the eye cannot 

 avoid them. 

 — remedied by With a view to soften the light of these lamps, shades have 

 reatsbader' ^^^'^ contrived, formed of materials whose transparency is 

 more or less Imperfect ; for instance, large cylinder", or spheres 

 of crape, gauze, or roughened glass. This contri -ace is very 

 useful, and deserves to be more generally adoptt,;! , it is even 

 of so great importance that we cannot take too iauv.h pains to 

 improve it, und recommend it to the public. 



Witk 



