24 
THE METEORIC SHOWER OF NOVEMBER. 1866. 
[Nature and Art, January .1, 1867. 
about the sun — tiny little planets, in fact, — and 
coming at times within the earth’s atmosphere ; 
sometimes falling to the earth in the form of those 
mysterious, half metallic, half stony little masses 
that we call aerolites. 
But if they be mere lumps of metal and stone, 
why do they shine out with such star-like brilliancy 1 
Are they always in a burning state, or do they take 
fire only when they come within our atmosphere 1 
The latter is undoubtedly the case ; the earth’s 
atmosphere is the cause of their inflammation. It 
would seem at first sight probable that this combus- 
tion had a chemical origin ; that the meteors were 
composed of some highly inflammable matter which 
is ignited by combination Avith the chemical com- 
ponents of the atmosphere. An idea of this kind 
pre\’ailed some years ago, but it is no longer neces- 
sary to resort to such a supposition ; for the ignition 
of the scraps of meteoric matter is amply accounted 
for by the mechanical theory of heat, according to 
which that ignition is a consequence of the immense 
resistance the bodies meet with in our atmosphere, 
and hence of the enormous friction and consequent 
heat produced thereby. Upon this point we cannot 
do better than quote the words of Dr. Joule, one 
of the famous exponents of this beautiful theory of 
mechanical heat. Our extract is from a lecture 
delivered at Manchester some twenty years ago, 
when this theory Avas first dawning upon philo- 
sophical minds : — 
“ From the velocity Avith which shooting stars 
travel, there can be little doubt that they are small 
planets Avhicli, in the course of their reA 7 olution 
round the sun, are attracted and drawn to the 
earth. Deflect for a moment on the consequences 
Avhicli would ensue if a hard meteoric stone Avere 
to strike the room in which we are assembled Avith 
a velocity sixty times as great as that of a cannon 
ball. The dire effects of such a collision are effec- 
tually prevented by the atmosphere which surrounds 
our globe, by Avhicli the velocity of the meteoric 
stone is checked, and its living force converted into 
heat, Avhich at last becomes so intense as to melt 
the body and dissipate it in fragments too small, 
probably, to be noticed in their fall to the ground. 
Hence it is that although multitudes of shooting 
stars appear every night, feAv meteoric stones have 
been found, those few corroborating the truth of 
our hypothesis by the marks of intense heat which 
they bear on their surfaces.” 
It seems anomalous that so soft and subtle a bed 
of matter as the air presents, especially in those 
exalted regions, should offer such a powerful resist- 
ance as to strike fire from a body coming into col- 
lision Avith it ; but the anomaly vanishes Avlien Ave 
bear in mind that this resistance is proportionate to 
the velocity of the body’s flight, and that this 
velocity, in the case of meteors, is upon the average 
about thirty miles in a second of time — a speed 
almost beyond human conception. Suppose, for 
example, that a meteoric stone six inches in 
diameter dashes into our atmosphere Avith a velocity 
of only eighteen miles in a second ; and suppose 
the atmosphere at fifty miles high to be 100 times 
less dense than at the earth’s surface. The resist- 
ance offered would be equal to a pressure of at least 
52,000 pounds ; and if the stone travelled tAventy 
miles with this resistance before it, sufficient heat 
would be developed to raise seven millions of pounds 
of Avater one degree- of temperature. The greater 
part of this intense heat is communicated to the 
displaced air, and hence the stone may be said to 
be in a soi’t of hot blast furnace. If only the one- 
hundredth part of the developed heat be received 
by the stone, it would still be more than amply 
sufficient to fuse and dissipate any materials of 
which it may be composed. 
We have here an example of one of those beauti- 
ful “provisions of nature” with Avhich the universe 
is filled. “Were it not” — we are again quoting 
Dr. Joule — “ for the atmosphere which covers us 
Avith a shield, impenetrable in proportion to the 
violence it is called upon to resist, Ave should be 
continually exposed to a bombardment of the most 
fatal and irresistible character. To say nothing of 
the larger stones, no ordinary buildings could afford 
shelter from veiy small particles striking at the 
velocity of eighteen miles per second. Even dust 
flying at such a A T elocity Avould kill any animal ex- 
posed to it.” 
Question begets question Avhen Ave cross-examine 
inexhaustible nature; and we are prompted to 
inquire Avhat is the nature and composition of 
these celestial fireworks 1 By analysis of their 
light, by means of the prism, Ave find that the burn- 
ing matter is sometimes of a metallic and some- 
times of an earthy or stony nature, and this in a 
measure identifies them Avith the stony-metallic 
masses that Ave knoAv to have falleu from the skies. 
It is pretty Avell established that there is a close con- 
nection between meteors and aerolites ; the one class 
of bodies merging imperceptibly into the other; and, 
therefore, in analysing the aerolite Ave may reckon 
upon gaining at least a probable knowledge of the 
constitution of the meteor. Chemists and mineralo- 
gists have frequently and Avith great care analysed 
aerolites and meteorites, and they have found that 
their composition is nearly always the same. Their 
structure, microscopically examined, sIioavs them to 
be composed of minute globules, which suggest the 
idea of an originally vanorous condition ; and their 
component matter is identical with that of earthly 
rocks and minerals. Sulphur and carbon, silica 
and alumina, iron — metallic and magnetic, — with 
other metals, such as nickel, cobalt, manganese, tin 
and copper, have been recognised among the materials 
of Avhich they are formed ; but — a fact striking and 
significant — no new material, no substance unknown 
upon the earth has ever yet been detected among 
the elements of their composition. Such a fact 
points to a unity of composition in some at least 
of the members of our planetary system, and 
favours the supposition of a common origin to all 
that family of bodies of Avhicli the sun is the grand 
centre and chief. 
We will pass now to the consideration of those 
periodic displays of meteors, that, from the abun- 
dance in Avhicli these bodies manifest themselves on 
