238 AKNUAL REPORT SMlTttSOKIAN INSTITUTION, 1942 



of the thick vegetation or the numerous rocks strewn over the surface. 

 In other areas conditions are ideal for easy recognition of a meteorite 

 on the ground. One reason why so many falls have been reported 

 from certain districts is that the inhabitants have been encouraged 

 to search for meteorites by being advised that these objects are easily 

 salable. Once the residents of a district know what a meteorite looks 

 like, and realize that there is a chance of monetary reward, it is likely 

 that new finds will be made. 



There have been so many meteorites reported from certain districts 

 that it has become necessary to exercise caution before announcing 

 a discovery as a new one. It is increasingly important that the exact 

 locality of the place of discovery be recorded; the old practice of 

 stating general localities such as counties no longer suffices to estab- 

 lish new falls. 



It is not only necessary to have a portion of any newly discovered 

 specimen examined in the laboratory, but it is also important to have 

 it examined where complete records of all falls are available, and 

 preferably where there is a large collection of meteoritic material 

 available for comparative study. Sections should be cut from the 

 mass to be compared with the other meteorites previously reported 

 from that area. Many meteorites are so similar in structure and 

 composition that even after these precautions are taken, it is difficult 

 to state definitely whether a particular specimen is a new discovery or 

 is merely a part of a fall previously recorded from that area. 



The United States National Museum has specimens of over 75 

 percent of all the reported meteorites from this country and nearly 

 55 percent of the total reported for the entire world. Thus excellent 

 reference material is available for the investigation of a newly dis- 

 covered fall. Individually all the specimens are not of equal impor- 

 tance, but collectively they are most important for the study of varia- 

 tions in the structure and composition of the different groups. Some 

 of the specimens weigh more than a ton, others but a few grams. It is 

 necessary, however, to have sizable samples in studying objects as 

 complex and varied as meteorites. 



FLIGHT OP A METEORITE 



At the time a meteor enters the outer atmosphere perhaps 40 miles 

 or more above the earth, its speed is known to be very great. The 

 slowing down of the rapidly moving object causes the mechanical 

 energy to be converted into heat with the result that the air com- 

 pressed in front of it becomes very hot. As the density of the air 

 increases, the velocity of the meteor is more retarded, and at the 

 same time the amount of heat thus generated rapidly increases. 

 When the falling body is within 6 to 9 miles of the earth's surface, its 

 velocity usually is so reduced that the generation of heat practically 



