84 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1961 



solar flare (3+ magnitude). The high tritium content and its 

 depth dependence in the satellite material lead to the conclusion that 

 the solar flare contains 0.4 percent tritium. This is the first meas- 

 urement of a radioactive isotope from the sun. 



Dr. Fireman completed measurements of argon-37, argon-39, and 

 tritium in several freshly fallen meteorites, and showed that the 

 cosmic-ray flux is higher at a distance of one astronomical unit from 

 the earth than at three. He has also obtained preliminary measure- 

 ments on radioactive isotopes in the Bruderheim meteorite. His 

 analysis of uranium, potassium, argon- 140, and krypton-xenon in 

 iron meteorites will help determine the age and early history of the 

 meteorites. 



Dr. Paul W. Hodge continues his study of the rate of accretion by 

 the earth of meteoritic matter and will determine especially the 

 physical and chemical properties of fine dust particles collected by 

 jet aircraft at altitudes varying from 30,000 to 90,000 feet. Collec- 

 tions at even greater heights, up to 250,000 feet, will be attempted. 



Dr. Richard E. McCrosky, with the collaboration of the Harvard 

 College Observatory, U.S. Air Force, Lincoln Laboratories, and Na- 

 tional Aeronautics and Space Administration, continues his attempt 

 to reproduce the meteor phenomena by a study of artificial meteors. 

 The results should help calibrate the mass-luminosity scale of natural 

 meteors. From a project designed to recover a larger number of 

 meteorites as soon as possible after their fall, Dr. McCrosky will seek 

 data on the cosmic-ray intensity in the vicinity of the earth and 

 throughout the orbit of the meteorite. His findings will add to our 

 present inadequate knowledge of the numbers, masses, and orbits 

 of meteorites. 



Dr. McCrosky continued his planning of a program to locate and 

 recover meteorites as soon as possible after their fall, by photograph- 

 ing meteors in flight and analyzing the photographic records to find 

 the place of fall. The program will also augment our knowledge 

 of the number, masses, and orbits of large meteors. Preliminary de- 

 sign of the stations is complete ; the general location of the stations 

 in the network in the Midwest has been determined; and a machine 

 program for computation of impact points has been completed. The 

 program has not yet received financial support. In view of the 

 scientific results that can be expected from this project, it should be 

 funded as soon as possible. 



Dr. F. Behn Riggs, Jr., designed and developed an electron probe 

 microanalyzer to make possible a point-by-point chemical analysis 

 of polished surfaces of sectioned meteorites without destruction of 

 samples. Analyses of micrometeorites, along with other experiments 

 in bringing the electron beam into the air, have resulted in a useful 

 evaluation of unsolved technical problems. 



