SECRETARY’S REPORT 99 
Meteoritical studies—Research in meteoritics has provided inval- 
uable information on the relation between meteors and comets, and 
the origin of comets. The Director’s analyses of data, based on his 
Icy Comet theory, have yielded more information on the nature 
and origin of comets, and possibly the origin of the solar system. 
Recent studies of micrometeorites in the earth’s atmosphere indicate 
that heavier elements, of the meteoritic category, condensed early in 
the original gases responsible for the formation of the cometary 
system and probably the planets. 
An electron probe microanalyzer, designed and developed by Dr. F. 
Behn Riggs, Jr., with Dr. Andrew R. Lang as consultant, for the 
study of meteorites, is expected to be in full operation in the fall. 
Electron probe microanalysis is one of the newest methods for chemical 
analysis. In addition to its use for point-to-point analysis of the 
metallic constituents of iron meteorites, the microanalyzer will permit 
study of the gross distribution of elements across the surface of a 
sectioned meteorite measuring up to ten inches across. The distribu- 
tion of elements cannot be measured on such a scale by any other 
method. 
The Director, Dr. Fireman, Dr. Frances W. Wright, Paul W. 
Hodge, Hai Chin Rhee, Kenneth Covey, and Adolph Esposito con- 
tinued the program of collection and identification of micrometeoritic 
dust. Collections of atmospheric particulate matter were made by 
high-flying jet aircraft. A collector mounted on a B-52 by the 
Boeing Aircraft Co. and flown by them has provided 19 exposed 
filters usable for analysis. ‘The filters have been examined optically 
under a high-powered microscope and particles of various descrip- 
tions have been identified and counted. Those particles which might 
be meteoritic have been listed for analysis; some have been used for 
chemical analysis; and the rest will be used in a general analysis of 
contamination problems. ‘The analysis of micrometeoritic dust in- 
dicates that these particles are magnetic and have more or less normal 
densities; tests for copper and nickel by neutron activation revealed 
that the sensitivity for copper was somewhat better than the value 
0.1 percent for 10p particles. The Massachusetts Institute of Tech- 
nology reactor and the counting equipment of the Observatory labo- 
ratory were used for the experiment. The development of new and 
improved types of dust collectors for high-altitude aircraft is a 
continuing part of this program. The most recent development is a 
cylindrical impactor. 
Dr. John Wood has investigated the various types of silicate me- 
teorites, particularly of chondrites. Analysis of thin sections of 
chondrites in polarized light with the petrographic microscope has 
shown that the petrographic characteristics of these meteorites do not 
