148 SCIENTIFIC AGRICULTURE. 



arc too dazzling to admit of their being seen. The most 

 probable cause of this phenomena is, that it depends on the 

 refraction of light in passing through small transparent prisms 

 of ice, floating in the higher regions of the atmosphere. 



PARHELIA. 



Parhelia, or mock suns, consist of the simultaneous appear- 

 ance of several images of the true sun. They are at the same 

 height above the horizon as the sun, and are connected by a 

 horizontal circle, which is sometimes colored, but usually white- 

 The cause of these suns is not satisfactorily explained : they 

 are supposed, however, to depend in some way upon the reflec- 

 tion and refraction of the sun's rays. There may be parhelia 

 without rings, and rings without parhelia. They never appear 

 in an unclouded sky, sometimes occur opposite to the sun. 



FIRE BALLS. 



These are "luminous bodies which suddenly appear in the 

 sky, usually at a great height above the earth, and shoot 

 through the heavens with immense velocity, and are sometimes 

 accompanied by the fall of an aerolite." Various hypotheses 

 have been proposed to account for these meteors : limit does 

 not admit of a detail of these opinions ; and it is perhaps suffi- 

 cient to say, that the true explanation of this phenomenon has 

 not, so far as we can ascertain, been given. 



RAINBOW. 



This well known and beautiful meteor consists of two con- 

 centric arches, formed of the colors of the solar spectrum. It 

 is caused by the refraction and reflection of the sun's rays 

 while falling on drops. of rain. The size of a rainbow depends 

 upon the height of the sun above the horizon. Inverted bows 

 are sometimes seen on the ground; they are formed by the 

 rays of the sun falling on the drops of dew or rain which are 

 suspended from the tops, of grass, or from spider' webs : they 



