206 
Hence we find that the ultimate temperature acquired by 
a body moving through air of whatever density is for the 
velocity of 39 miles per second 2000000° C. The question 
to be solved is whether at the known height of meteors, 
as above stated, the density of the air is sufficient to 
give rise to effects in quantity sufficient to account for the 
actual phenomena. 
Now if we reckon the decrease of density to be one 
quarter for every seven miles, we shall find the quantity 
of air in a column of, say a mile long and one square foot 
section, to be about ’0003 of a grain at the height of 116 
miles, the elevation at which meteors in general are first 
observed. The temperature acquired at the surface of a 
meteorite of a foot section and of the specific heat '23, moving 
at the average velocity at the average highest elevation through 
one mile, will be ’0003 gr. raised 2000000° C., or otherwise 
'2 gr. raised 3000° C. which would be doubtless able to fuse 
any known substance, and bring it to a condition of dazzling 
brilliancy. The meteorite of a foot section might, I believe, 
have iitli of a grain of its surface brought to this condition 
in its passage of one mile in the - 3 Vth of a second. I do not 
think that the luminous effect would be neutralised by con- 
duction of heat to the interior of the meteorite, as it is very 
likely that the spheroidal condition would be produced. I 
can therefore easily believe that the ith grain at 3000° C. 
would give sufficient light to attract an observer at the 
distance of 100 or 200 miles. 
From data given in Hersclicl’s Outlines of Astronomy” 1 
find that, at the elevation and velocity above stated, viz., 116 
and 39, and supposing as before the entire effect to be given 
out by radiation, a meteorite of .five feet diameter would have 
the brilliancy of a Centauri. 
As the meteorite descends towards the earth its brilliancy 
will increase to a certain point, when, from the quantity of 
fused matter, a longer tail will be left behind. This process 
will of course be sustained for a longer time by the larger 
meteorites, which are thus enabled to penetrate to a nearer 
distance from the earth’s surface. 
