THE EARTH VIBRATES CONTINUOUSLY even without help from earthquakes. A collaboration of scientists from UC Santa Barbara and Tokyo Institute of Technology has analyzed gravimeter data from 1983 to 1994 and found 61 days to be seismically "quiet" enough for the purpose of searching out Earth's natural oscillation modes. They identify several such modes in the 2 to 7 milli-Hz range (that is, vibrations with periods of hundreds of seconds). The acceleration of material in the solid Earth produced by these spheroidal waves is tiny, on the order of nano-gals, or 10^-9 cm/sec². The researchers suspect that the cause of the vibrations is atmospheric turbulence. (Tanimoto et al., Geophysical Research Lett., May 15; contact Toshiro Tanimoto, UC Santa Barbara, toshiro@magic.geol.ucsb.edu.)