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TEE AMERICAN MUSEUM JOURNAL 



they become broken into a few pieces 

 only, which survive further crushing. 



Metallic iron is however so freely 

 combustible that when exposed to a 

 blast of hot, compressed oxygen, it is 

 burned into fused iron oxide very rap- 

 idly. That is what happens to iron 

 meteors in their flight. The air in front 

 of them is like a blast of highly com- 

 pressed gas so rich in oxygen, and so 

 heated by compression, as to cause the 

 iron to burn like tinder. The survival 

 of a stony meteor or aerolite for such a 

 time that it may reach the ground, 

 must consequently result from its hav- 

 ing entered our outer air at a compara- 

 tively low velocity— or upon its having 

 had a long flight almost horizontally in 

 the thinnest outer air, so that much of 

 its initial speed was lost before it fell 

 into the denser air below. On the other 

 hand, the survival of an iron meteorite 

 or siderite depends on its velocity being 

 insufficient to develop crushing strains 

 ffreat enough to fracture it into small 

 pieces, and upon the size of the mete- 

 oric mass itself, or of its fragments, if 

 fractured. A small iron mass of high 

 velocity will burn away so rapidly in 

 the dense oxygen in front of it that the 

 whole mass will be consumed and dis- 

 sipated before any of it reaches the 

 ground. Moreover, the energy of mo- 

 tion converted into heat by air resist- 

 ance will not heat the body internally. 

 The heat will be in the fused outer skin 

 of oxide and will go into the trail or 

 train left behind in the meteor's path. 

 Indeed, the fused iron oxide as soon as 

 formed on the outer surface is blown off 

 and left behind in the hot luminous 

 trail which marks the course of the 

 body through the air. 



If, however, the iron mass or frag- 

 ment is large and the velocity has been 

 reduced so that no further crushing or 

 breaking can occur, then although rap- 



idly burning on its surface, the time of 

 flight being short, a considerable frac- 

 tion of it may reach the ground or the 

 sea surface while still moving with con- 

 siderable velocity. On the land it may 

 bury itself to a depth more or less grea+. 

 In the case of an iron meteorite just 

 considered, there will then be two 

 sources of heat energy giving rise to 

 luminosity. The air in front will be 

 highly compressed and luminous while 

 the wastage by combustion of the iron 

 on the outer surface will result in high 

 luminosity and a train of sparks or fire 

 with a more ruddy light back of the 

 meteor. 



The recent industrial use of the 

 acetylene blowpipe with excess of com- 

 pressed oxygen in cutting heavy iron 

 and steel masses, such as thick plates, is 

 an evidence of the effectiveness of the 

 combustion of iron in removing mate- 

 rial. The product is of course mag- 

 netic oxide, a black oxide of iron in a 

 fused state which is blown away as fast 

 as it is formed, thus continually expos- 

 ing unoxidized metal to continue the 

 Inirning. Melted pear-shaped drops 

 have indeed been observed falling out 

 of the track or train left by an iron 

 meteor in its course through the air. 

 These are probably composed of iron 

 cinder or melted oxide. 



The flight of a meteor is so short in 

 time that although its surface is highly 

 heated, it has not sufficient heat con- 

 ductivity to allow heat to pass from its 

 outer surface to the interior. It enters 

 the air in a very cold state and at no 

 time possesses more than a thin skin of 

 heated metal, which at once burns, 

 liquefies, and is torn off. It can only 

 possess, as it were, a thin laver in which 

 the temperature gradient is very sharp 

 or steep. The temperature limit of 

 this layer or skin is the melting point of 

 the oxide or of the iron itself, for, as 



