240 AOTSrUAL REPORT SMITHSONIAN ESTSTITDTION, 1942 



wide, others narrow and deep, and examples are known in which a 

 hole pierces the entire mass. It is sometimes possible to determine 

 the direction of the air flow by rubbing one's hand over the surface of 

 the meteorite. The surface feels smoothest when the motion of the 

 hand is in the same direction as the air flow, a decided difference be- 

 ing sometimes felt on rubbing the surface in the opposite direction. 



When the Reed City iron was sectioned in our laboratories, a number 

 of slices exhibited areas on the edge where heat had locally disrupted 

 the internal structural pattern. A thin film of black solidified liquid 

 oxide lies between the granular area and the normal octahedrite 

 structure. This oxide film (pi. 4) must mean that there was a small 

 invasion of melted oxide and iron, the latter developing a granular 

 structure in cooling. If the mass had remained in a fixed position 

 a little longer, perhaps this granular portion would have been swept 

 out, deepening the depression and also making possible the forma- 

 tion of whirlpools of air which would further abrade the meteorite, 

 forming the pits common on so many irons. Unfortunately these 

 structural features were not observed until the individual specimen 

 had been cut into sections so it is impossible to relate this structure 

 to any flight markings that may have been on the surface of the 

 specimen. 



The air does an effective piece of work in rubbing out these celestial 

 bombs. Their size when they first enter our atmosphere is not known 

 with any accuracy, but there is reason to believe they are sometimes 

 very large. Records of different falls show that very few large ones 

 get through to the earth, and we should indeed be thankful that the 

 air is such an effective screen against meteoritic bombs. The total 

 weight of material in any shower may be large but it is unusual to 

 find individual specimens weighing as much as 500 pounds. Good 

 observations on the Chicora, Pa., fall indicate that a large mass did 

 survive the passage through the atmosphere until it reached a level 

 of about 12 miles above the earth. At this point something happened 

 — probably the mass was crushed by the pressure of the resisting air. 

 Calculations based upon direct observations indicate that at the 

 12-mile level the mass must have weighed in the neighborhood of 

 500 tons. Only 303 grams of this meteorite are known to have reached 

 the earth, which is indeed a very small fraction of what existed 12 

 miles up. 



In a few widely scattered localities on this earth, large holes bear 

 witness to the crash of super-meteorites. All but one of these occurred 

 before the dawn of recorded history; consequently we know nothing 

 regarding the frequency of such events. One of these super-meteorites 

 that did fall in our time — the Tunguska meteorite which crashed 

 down on Siberia on June 30, 1908 — really gave our world a good rap. 

 European seismographs recorded a strong ground wave, and baro- 



