186 MIRAGE. 



coss from each other, whence it appears that a shower of 

 stones in this instance took place. The fragments amounted 

 to several pounds in weight. One weighed nearly one 

 pound six ounces avoirdupois, and exactly resembled a bodj' 

 coated with black paint or pitch. Its interior was of an ash- 

 gray colour, and contained imbedded metallic-looking parti- 

 cles. Its specific gravity is stated as varjing from 3.352 

 to 4.281. On the night of the 7th August, 1822, a me- 

 teoric stone fell near the village of Kadonah, in the district 

 of Agra, with much noise as of cannon, the wind awaken- 

 ing those who were asleep, and alarming a watchman who 

 heard it fall ; on making search in the morning it was found 

 warm, and with little smoke rising from it. The stone was 

 shown in London in 1827. Several stones fell in the dis- 

 trict of Azim Gerh on the 27th Februar}-, 1827. 



These fire-balls, and the meteoric stones they drop, are 

 considered as formed in the earth's atmosphere, and there- 

 fore as of tellurian atmospherical origin. 



15. Mirage. — On viewing distant objects, it often hap- 

 pens, under certain circumstances, that these objects pre- 

 sent many images which are straight, oblique, or inverted, 

 and always more or less changed in the contour. It is the 

 appearance of these images, without any visible reflector to 

 produce them, which constitutes mirage. In explanation 

 of this phenomenon it may be remarked, that as- soon as 

 the soil becomes heated, the lower stratum of air is also af- 

 fected by the calorific influence. Numerous aerial currents 

 are established, and an undulatorj' motion takmg place in 

 the air, distant objects become changed in form, and va- 

 riously distorted and bi'oken. If when these changes are 

 going on a calm should prevail, and the mass of atmosphere 

 upon the plain remain at rest while the stratum in contact 

 with the ground becomes gradually heated, mirage will arise. 

 In such cases the observer will see distant objects in their 

 natural positions and forms ; but bclaw them their images 

 will be seen reversed, and the spectator believe that he is 

 looking at a reflection from the surface of a body of water. 

 The sky also joins in completing the illusion, its image be- 

 ing reflected in the same manner. The whole visible ap- 

 pearances, the French philosophers who visited Egypt re- 

 mark, are mdeed the same as those usually exhibited by 

 water. All the laws by which the obsener has been accus- 



