444 
The theory which attributes falling stars, fire-balls, and me- 
teoric stones, to the attraction of minute planetary or cometary 
bodies revolving round the sun, within the sphere of attrac- 
tion, seems to be the following. An immense number of such 
bodies are scattered through what is called inter-planetary 
space. When these bodies are drawn within the sphere of 
the earth's attraction by its disturbing force pulling them out 
of their orbit, they enter within the limits of the earth s at- 
mosphere. Coming into this atmosphere, even where, fiom its 
height above the earth's surface, it is very greatly attenuated, 
nevertheless, the friction produced by their passing through 
this attenuated atmosphere, with their own planetary velocity 
of motion, combined in most instances with that oi the earth 
itself, produces such an enormous heat as to inflame the 
matter composing the body, and in most instances to convex 
all its solid particles into vapour. A falling star, therefore, is 
caused by the passage of an inter-planetary body with enor- 
mous velocity through the earth's atmosphere, causing its rapid 
combustion and speedy dissipation into vapour. Attempts 
have been made (though I cannot but regard all such calcula- 
tions as most fallacious) to calculate the velocity necessary to 
produce the combustion of a meteoric mass, such as a meteo- 
rite, at some forty or fifty, or even a hundred miles height 
from the earth's surface, and the light which would be emitted 
bv a given mass of matter; this, too, in spite of our admitted 
ignorance of the density, or rather tenuity, of the atmosphere 
at such heights. „ _ , . , 
Some of these bodies are supposed not to be entirely con- 
sumed, but their apparent track as a luminous body is sup- 
posed again to be produced by their passage through a portion 
of the earth’s atmosphere, as they dip only through a part of 
the atmosphere in their motion through space. According to 
this theory, other flaming meteors or fire-balls consist of masses 
of matter too large to be so dissipated into vapour, which move 
for a longer time through the lower regions of the earth s 
atmosphere, till the nucleus of the meteor bursts by the action 
of intense heat, and meteoric stones and masses fail to tlie 
The wandering small planetary bodies are supposed to be 
more thickly distributed in some parts of space than others, 
like the ring of known and observed planetoids between Mai s 
and Jupiter. Two or more such rings are supposed to inter- 
sect the earth’s path. Such a ring would be subject to per- 
turbation by the earth’s attraction, causing a change m the 
periods at which it would intersect the earth s orbit. _we 
star-showers are supposed only to occur when a rich or thick 5 
