Phenomena of Falling Meteorites .— Farrington. 85 
2. “Is not the noise clue to the atmospheric agitation pro¬ 
duced by the impact?” This point will be discussed later. 
3. “Is there anything naturally or possibly explosive in the 
interior of the meteorite?” Yes. (a) The heterogeneous min¬ 
erals making up the mass of a meteorite possess different 
degrees of conductivity and vary as to their coefficients of 
expansion. Some, of them contain gas and perhaps liquid in¬ 
clusions. The effect of heating the surface of such a mass to 
incandescence, while its interior remains cold, will be to gen¬ 
erate internal strains quite similar to those produced in a 
glass rod when its exterior is suddenly heated. The same re¬ 
sult, therefore, may be expected,—the mass will fly to pieces. 
The bursting, often with considerable violence, of stones when 
heated is a phenomenon familiar to any farmer’s boy who has 
built a fire near a rock, or dropped a stone into a fire; and, 
except that the heat is much less intense and therefore a less 
violent action can be expected, it is quite the analogue of the 
explosion of a meteorite, (b) The gases occluded in meteorites, 
often under considerable pressure (Handbook, p. 18), would, 
when suddenly expanded by heat, tend to rend the mass in 
which they were enclosed. 
1. “Is not the fact that the interior of the mass is usually 
cold, sufficient demonstration that the exterior only has been 
heated and hence, also, that it has suffered the greater amount 
of expansion?” 
It is probably true, except in the metallic meteorites, that 
the exterior only is heated, but this very contrast of tempera¬ 
ture is just what is required to bring about the conditions of 
strain and forces producing rupture referred to above. 
5. “In the firing of a cannon is it the ‘explosion’ proper 
that is heard, or is it the atmospheric undulation which is 
produced by the rush of the column of liberated gas into the 
still air?” . 
For the production of sound three elements are necessary, a 
vibrating body, a conducting medium and a receiver. When 
gunpowder is fired the sudden expansion and immediate con¬ 
traction of the gases generated set the air in vibration and 
produce upon the ear the sensation of sound. “The ‘explo¬ 
sion’ proper” that is heard, therefore, is the atmospheric un¬ 
dulation produced by the sudden expansion and contraction 
of the air. If not, what is it? 
