Prof. Maskelyne and Dr. Lang's Miner alogical Notes. 57 



it is as difficult to get a clear conception as is that velocity itself. 

 The intense heat instantaneously developed on the surface of 

 the mass will assuredly be sufficient to melt that surface down 

 into an enamel, before it could have time to penetrate to even 

 a sensible depth into the body. If, as is probable, this fused and 

 white-hot enamel flies off from the mass as it proceeds with the 

 scream of a huge projectile through the air, its place will be 

 continually taken by a fresh and continuously flowing stream of 

 the same incandescent material. That material, too, is com- 

 bustible. The metallic iron in many an aerolite ranges above 

 20 per cent., and is associated with sulphur as pyrites, and 

 sometimes in other forms. Here at least is cause for much, 

 if not a sufficient cause for the whole, of the spectacle exhibited 

 by the blaze of a meteor. That the air itself is also heated to 

 whiteness, and as such becomes visible, as Haidinger suggests, 

 is highly probable, and would add still more to the brilliancy 

 of the light. 



But while the enormous velocity of the body is thus instanta- 

 neously arrested and converted into heat, the effect of that heat 

 will not be exhibited in the molten spray of enamel alone. The 

 heated surface will gradually, but by no means slowly, impart 

 its heat to the interior ; and notwithstanding the non-conducting 

 character of the stony ingredients of an aerolite, the outer por- 

 tions (a sort of shell around it) will rapidly rise in temperature. 

 The coldness of the interior would only gradually be overcome, 

 and, long before it would be so, the expansion of the external 

 parts would tend to tear them away from a contracted and far 

 more than ice-cold core within. The limits and the form of that 

 core, the conditions under which disruption would ensue (indeed, 

 whether it would ensue at all, as it would not if the mass were 

 absolutely homogeneous), would depend on the structure of the 

 mass, its directions or planes of weaker aggregation, or perhaps 

 the unequal distribution in it of matter of various degrees of 

 conductibility. But when the disruption comes, it must come 

 with explosion. 



The process may be repeated, or it may take place at different 

 intervals on the different sides of the meteorite. The earlier 

 explosions may take place at points in its path where there is 

 still velocity enough to produce a fresh enameling, — sometimes 

 in a copious flow, at others only enough to barely glaze the ex- 

 posed surface of the stone again ; the later ones may occur when 

 the velocity is more nearly spent, and the friction is no longer 

 competent to generate the glaze. 



The cloud in the air, out of which the meteorite has been seen 

 to come in so many authenticated instances, would be satis- 



