THE ANALYSIS OF LIGHT. 

 Fig. 273. 



337 



The production of halos may be illustrated experimentally, by crystallizing 

 various salts upon plates of glas.s, and looking through the plates at the sun, 

 or a candle. A few drops of a saturated solution of alum, spread over a 

 glass so as to crystallize quickly, will cover it with an imperfect crust of crys- 

 tals, scarcely visible to the eye. Upon looking at a luminous body through 

 the glass plate, with the smooth side next the eye, three fine halos will be 

 perceived encircling the source of light. 



The flict that halos, or rings round the moon, are more frequently observed 

 than solar halos, is dependent upon the circumstance th.at the sun's light ia 

 too intense and dazzling to allow the halo to be recognized. Halos may be 

 observed most frequently in the winter S3ason, and in high northern latitudes. 



696. The beautiful crimson appearance of 

 the clouds after sunset in the western horizon, 

 is due in a great measure to the fact that the 

 red rays of the solar light are less refrangible 



than any of the 

 other colored rays, 

 and in conse- 

 quence of this, 

 they are not bent 

 out of their course 

 so much as the 

 blue and yellow 

 s rays, and are the 

 ^^^ last to disappear. 

 '"^^0^ For the same rea- 

 ls 



What is tha 

 occasion of the 

 red appearance 

 of tho clouds at 

 Eunrise and 

 fiUQset 1 



Fig. 



