THE AUGUST AND NOVEMBER METEORS. 387 



light; under similar circumstances a lead bullet becomes partially 

 melted. The heat of a body consists in the vibratory motion of its 

 smallest particles ; an increase of this molecular motion is synonymous 

 with a higher temperature; a lessening of this vibration is termed de- 

 creasing heat, or the process of cooling. Now, if a body in motion, as 

 for instance a cannon-ball, strike against an iron plate, or a meteorite 

 against the earth's atmosphere, in proportion as the motion of the body 

 diminishes and the external action of the moving mass becomes annihi- 

 lated by the pressure of the opposing medium upon the foremost mole- 

 cules, the vibration of these particles increases ; this motion is immedi- 

 ately communicated to the rest of the mass, and by the acceleration of 

 this vibration through all the particles the temperature of the body is 

 raised. This phenomenon, which always takes place when the motion 

 of a body is interrupted, is designated by the expression the conversion 

 of the motion of the mass into molecular action or heat / it is a law 

 without exception that, where the external motion of the mass is dimin- 

 ished, an inner action among its particles, or heat, is set up in its place 

 as an equivalent, and it may be easily supposed that, even in the high- 

 est and most rarefied strata of the earth's atmosphere, the velocity of 

 the meteorite would be rapidly diminished by its opposing action, so 

 that shortly after entering our atmosphere the vibration of the inner 

 particles would become accelerated to such a degree as to raise them to 

 a white heat, when they would either become partially fused, or, if the 

 meteorite were sufficiently small, it would be dissipated into vapor, and 

 leave a luminous track behind it of glowing vapors. 



Haidinger, in a theory embracing all the phenomena of meteorites, 

 explains the formation of a ball of fire round the meteor, by supposing 

 that the meteorite, in consequence of its rapid motion through the 

 atmosphere, presses the air before it till it becomes luminous. The 

 compressed air in which the solid particles of the surface of the meteor- 

 ite glow then rushes on all sides, but especially over the surface of the 

 meteor behind it, where it encloses a pear-shaped vacuum which has 

 been left by the meteorite, and so appears to the observer as a ball of 

 fire. If several bodies enter the earth's atmosphere in this way at the 

 same time, the largest among them precedes the others, because the air 

 offers the least resistance to its proportionately smallest surface ; the 

 rest follow in the track of the first meteor, which is the only one sur- 

 rounded by a ball of fire. When by the resistance of the air the mo- 

 tion of the meteor is arrested, it remains for a moment perfectly still ; 

 the ball of fire is extinguished, the surrounding air rushes suddenly 

 into the vacuum behind the meteor, which, left solely to the action of 

 gravitation, falls vertically to the earth. The loud, detonating noiso 

 usually accompanying this phenomenon finds an easy explanation in 

 the violent concussion of the air behind the meteor, while the generally- 

 received theory, that the detonating noise is the result of an explosion 

 or bursting of the meteorite, does not meet with any confirmation. 



