Number 75, April 10, 1992 by Phillip F. Schewe and Ben Stein A TWO-PHOTON OPTICAL LASER has been developed by Thomas Mossberg at the University of Oregon (Physical Review Letters, 27 Jan. 1992). In this laser system, a beam of barium atoms is pumped by a laser beam tuned to excite the atoms to special doublet states. A separate trigger laser beam, parallel to the main cavity and at right angles to both the barium beam and the pump beam, initiates a laser action in which the barium atoms emit not one but two photons simultaneously. A plot of the two-photon power intensity as a function of time shows a small, unexplainable oscillation. (Physics World, April 1992.) EARTH'S INNER CORE OSCILLATES SLIGHTLY , according to new sensitive gravity measurements by Douglas E. Smylie at York University in Ontario and by scientists at other labs. Smylie's gravimeter used superconducting magnets to levitate a small niobium ball, whose motion, sensitive to the tug of a slightly changing gravitational field, provides a measure of possible pendulum-like oscillations of the Earth's solid core within the fluid medium of the outer core. Using his own data and data from gravimeters in Brussels, Frankfurt, and Strasbourg, Smylie has deduced three translational modes for the inner core with periods of 3.58, 3.77, and 4.01 hours. Smylie has also used this information to calculate a density of 12.96 g/cm3 and a radius of 1221 km for the Earth's core. The gravimeters, it should be noted, can measure changes in gravity down to the level of a nanoGal (10-9 Gal, where Gal is the unit of acceleration, 1 cm/sec2, named after Galileo). In these units the gravity at the Earth's surface is about 1000 Gal. Thus the gravimeter can measure the difference in gravity brought about by lifting the device up by a distance equal the width of a human hair. (Science, 27 Mar. 1992) THE MAGNETIC HISTORY OF STARS can be pieced together from measurements of calcium radiation. The magnetic field of the nearest star, the Sun, can be monitored by counting sunspots or by measuring the splitting of certain spectral lines in the Sun's spectrum; the size of this "Zeeman splitting" is related to the size of the Sun's magnetic field. These methods don't work for faraway stars. Instead, calcium emission, which goes up with magnetic activity, is used as a substitute. With more than 25 years of data, astronomers have observed that some stars are undergoing periods of low magnetic activity, periods like the "Maunder minimum" when (in the late 1600's, the time of the Little Ice Age) our Sun had fewer sunspots and, as a consequence some believe, a slightly smaller brightness. Middle-aged stars like the Sun seem to spend about one third of their time in Maunder minima, the data show. Longer-term studies of stars' magnetic activity may thus tell us more about the history of the Sun and might provide insights into possible climate change here on Earth. (Astronomy, April 1992.) BUCKYBALL POLYMERS can be formed from C-60 molecules and palladium atoms. Scientists at Toyohashi University and the Mie University in Japan have prepared one-, two-, and three-dimensional compounds with polymer properties. The latter, C60Pd3, unlike the superconducting compound C60K3, is stable in air. (New Scientist, 28 Mar. 1992.)