98 B. V. Marsh on the Luminosity of Meteors. 
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If, as above maintained, the observed splendor is not due to _ 
the cenereians of the meteoric bodies themselves, but to thatof — 
mere envelopes of air, brought to the most intense degree of in- : 
candescence by the development of their latent heat, it is evident, 
that, inasmuch as this heat is nearly constant for all considerable 
heights, the most splendid results must be developed in the rarest 
fe ace of the atmosphere, because there the mass of the air to 
acted upon by ibis. fixed amount of heat is least; and thatas 
a poin be reached where the mass is so great 
that ‘lon, womans will “fall short of that required to produce in- 
candescence, and all luminosity must instantly cease. Theme — 
teor will then have ‘entered a medium whi ch has not the een 
ments necessary to its continued brilliancy.” 
The table shows that at the height of 10} miles, with the 
assumed degree of condensation, ve intensity ; will not pepe 
one thousand degrees, even without making any allowance for — 
the portion of heat which must pa eon be absorbed by the _ 
meteor itself. Luminosity must therefore cease above this limit, 
and the meteor must perform the remainder of its journey to a 
a pi as a dark body, unless the velocity be such as to pro 
duce uch greater condensation. The daylight meteor of a 
Hoveaier 15, 1859, owing to its amazing velocity, passed this 
limit, disappearing at the height of only six or eight miles with: 
out any perceptible diminution of velocity, but this is believ 
to be a rare instance. 
Whilst the luminous track of those meteors which have their 
g power and very @ 
Bra ase eat rh first eatedug the atmosphere abs 
so large a a portion o of the whole heat d as to prev 
of luminosity until a very considerable 
