72 ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 7 



findings strongly suggest that the meteorite approached the crater 

 from a direction slightly to the south of west rather than a north- 

 northwesterly direction, as has been previously assumed. The total 

 amount of finely divided meteoritic material was found to be about 

 12,000 ordinary tons, which fixes a lower limit to the mass of the 

 meteorite that formed the crater. The expedition was supported in 

 part by the Geophysics Kesearch Directorate of the Air Force Cam- 

 bridge Research Center. 



A concentrated effort is now being made to estimate the rate of 

 accretion of meteoric material by the earth and to establish the physi- 

 cal nature of this material. Most of the mass is probably accreted in 

 the form of dust and small particles. From a practical point of view, 

 astronautical ventures and possibly rainfall could be influenced by 

 such material. Thus far a few collections of dust (presumably 

 meteoric) have been made on the ground. A method will be devised 

 and a device constructed for collecting micrometeorites from aircraft 

 and balloons at and above stratospheric altitudes. The designs of 

 collectors are well underway, and an Air Force-furnished aircraft is 

 in sight for use in making collections. Paul Hodge is working ac- 

 tively on this project. 



Dr. E. L. Fireman is continuing his ground-breaking studies of the 

 stable and radioactive isotopes produced by cosmic rays in meteorites 

 and by high-energy particles in targets. Previously he conducted this 

 research at the Brookhaven National Laboratory. Part of the equip- 

 ment used for these studies has beeen transferred from Brookhaven 

 under a research contract with the Atomic Energy Commission and 

 put into operation at the Astrophysical Observatory, where a 

 radiochemistry laboratory has been set up. Dr. Fireman also col- 

 laborated with Dr. J. Zahringer to measure the depth variation of 

 tritium and argon-37 produced by high-energy protons in iron. 



Dr. Luigi G. Jacchia has supervised the reduction by accurate tech- 

 niques of meteors photographed with the Super- Schmidt cameras un- 

 der the Harvard Meteor Program and has conducted research on the 

 physical nature of meteors through a study of their deceleration and 

 fragmentation inside the earth's atmosphere. Among the significant 

 results of this research in the course of the elapsed year can be listed 

 the finding that there is no clear-cut evidence for the presence of hard- 

 bodied meteors of asteroidal origin among 361 Super-Schmidt meteors 

 which were analyzed, and the result of the comparison of visual and 

 photographic magnitudes of meteors, which showed that the "color 

 index" of meteors is rather independent of velocity, but shows a strong 

 dependence on meteor brightness. 



Upper atmosphere and satellite-tracking programs. — The respon- 

 sibility for the optical tracking of the IGY earth satellites was as- 



