COMMON THINGS COLOUR, 



specula, and all that would be visible would be the multiplied 

 reflections of the artificial lights. 



Irregular reflection, then, alone renders the forms and qualities 

 of objects visible. It is not, however, merely by the first irre- 

 gular reflection of light proceeding from luminaries by which 

 this is effected. Objects illuminated and reflecting irregularly the 

 light from their surfaces, become themselves, so to speak, second- 

 ary luminaries, by which other objects not within the direct 

 influence of any luminary, are enlightened, and these in their 

 turn reflecting light irregularly from their surfaces, illuminate 

 others, which again perform the same part to another series of 

 objects. Thus light is reverberated from object to object through 

 an infinite series of reflections, so as to render innumerable objects 

 visible which are altogether removed from the direct influence of 

 any natural or artificial source of light. 



13. The globe of the earth is surrounded with a mass of atmos- 

 phere extending forty or fifty miles above the surface. 



The mass of air which thus envelopes the hemisphere of the 

 earth presented towards the sun, is strongly illuminated by the 

 solar light, and, like all other bodies, reflects irregularly this 

 light. Each particle of air thus becomes a luminous centre, 

 from which light radiates in every direction. In this manner, 

 the atmosphere diffuses in all directions the light of the sun 

 by irregular reflection. "Were it not for this, the sun's light 

 could only penetrate those spaces which are directly accessible 

 to his rays. Thus, the sun shining upon the window of an 

 apartment would illuminate just so much of that apartment as 

 would be exposed to his direct rays, the rest remaining in 

 darkness. But we find, on the contrary, that although that 

 part of the room upon which the sun directly shines is more 

 brilliantly illuminated than the surrounding parts, these latter 

 are nevertheless strongly illuminated. All this light proceeds 

 from the irregular reflection of the mass of atmosphere just 

 mentioned. 



