100 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
appear to support the existence of primary bodies which antedated 
the parent meteorite planets. 
Under the supervision of Dr. Luigi G. Jacchia, the precise reduction 
and analysis of photographic meteor trails have shown that practically 
all the visual meteors are cometary in origin; fewer than 1 percent 
are interstellar in origin, and the contribution from asteroidal sources 
is probably not much greater. 
Under the supervision of the Director, Robert Briggs is studying 
the distribution of interplanetary dust particles to measure the num- 
ber of particles in various parts of the solar system. 
Dr. Fireman completed measurements of helium 3 in the Grant, 
N. Mex., meteorite and has determined its original mass (E. L. Fire- 
man, Planetary and Space Science, vol. 1, pp 66-70, 1959). The 
helium 8 contents ranged from 6.5X10-* em #/g to 5.110 cm $/g. 
The Grant meteorite apparently was a pear-shaped object in space, 
with a mass of approximately 880 kg; its loss of mass during its 
plunge through the earth’s atmosphere was approximately 400 kg. 
Dr. Fireman continued his measurement of the tritium, helium 38, and 
argon 39 in three stone and seven iron meteorites (KE. L. Fireman and 
J. De Felice, Astron. Journ. vol. 64, p. 127, 1959; also Geochim. et 
Cosmochim. Acta, in press). The argon-exposure age of these me- 
teorites ranges from 107 years to 6X10% years. This exposure age 
has been interpreted in terms of space erosion (F. L. Whipple and 
K. L. Fireman, Nature, vol. 188, p. 1815, 1959) and leads to the value 
1.5107 cm/year, for the upper limit of total erosion on an iron 
surface in space. 
Satellite-tracking program.—The network of 12 satellite-tracking 
stations, under the supervision of Dr. Hynek, has gathered photo- 
graphic data on the positions of artificial satellites. These data have 
allowed precision determination of the orbits of satellites and have 
thus provided geophysical and geodetic information. Seven objects 
were tracked. A total of 2,902 successful observations and more than 
6,000 photographs were obtained. Engineering studies were begun 
to improve both the Baker-Nunn camera and the timing system, to 
refine the photography of orbiting objects. The stations were manned 
by 38 observers. 
The Baker-Nunn camera has produced results of inestimable scien- 
tific value. The cameras are able to photograph stars to magnitude 
12.0 with an effective exposure time of 1 second. Tracking accuracy 
ranges between 1 percent and 5 percent. The ultimate limiting magni- 
tude, established principally by the time required to record appreciable 
skyfog, is about 16.0. The Baker-Nunn cameras secured photographs 
of the Vanguard experimental sphere, 1958 Beta Two, at ranges beyond 
2,400 miles. These cameras also obtained photographs of the carrier 
