6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IIO 



of an imperfectly transformed gamma-alpha mixture, appearing black 

 and unresolved except at high magnifications, the dark interiors often 

 being traversed or even filled w^ith oriented lamellae of kamacite. 



At the edge of one slice a zone of heat alteration was observed, 

 the normal structure being obliterated by secondary granulation. 



This meteorite must have struck the earth w^ith considerable force, 

 but neither the surrounding area nor the specimen itself showed any 

 indication of where or how this energy was dissipated. The prob- 

 lem of how much kinetic energy this mass would have had as 

 it struck the earth, assuming the meteorite as falling from a height 

 of 10 miles and starting with o velocity, was presented to L. B. Al- 

 drich. Director of the Smithsonian Astrophysical Observatory. His 

 reply is as follows : 



The magnitude of the air resistance in the fall of your meteorite from lo miles 

 up is very uncertain. If we assume no air resistance, the lO-mile fall would take 

 57 seconds and its velocity on reaching the earth would be 1,840 feet per second. 

 Its kinetic energy would be 61 million foot-pounds, or 84 million joules. These 

 are computed from the well-known formulae: 



V = Vo + af 



S—Vot + iar- 



Kinetic Energy := ^ MF^ 



where V = velocity, t = time, s ^= distance, M = mass, and a = acceleration 

 due to gravity. 



Actually, of course, the kinetic energy on reaching the earth would be ap- 

 preciably less because of air resistance. A. F. Zahm some years ago, using 4-inch 

 spheres as projectiles, experimentally determined air resistances for velocities 

 up to 1,000 feet per second. Applying his values to the meteorite I compute 

 that it would take approximately 70 seconds to fall and its kinetic energy would 

 be about 18 million foot-pounds. 



Two uncertain factors enter, however: (i) Air at 10 miles altitude is much 

 less dense than lower down. Thus the computed value is too small. (2) The 

 meteorite is not a sphere, but a rough, irregular mass. This would make the 

 computed K.E. too much. My guess is that the meteorite's K.E. would be per- 

 haps in the order of 20 million foot-pounds. 



We know the meteorite started much higher than 10 miles up and 

 that it had an initial velocity much greater than zero assumed for this 

 problem. However, before the mass hit the earth it had attained its 

 maximum velocity and in fact must have been slightly retarded. Yet 

 when this 1,164-pound iron was found it was resting almost entirely 

 on the surface of the groimd. True, it may have come to rest after 

 striking elsewhere, but no crater was found in that vicinity. 



There is only one place where the meteorite exhibits any distorted 

 metal that may mark the place on the sample which came in contact 

 with the ground at the moment of impact. One would certainly think 



