may be yielding to scientific investigation. Researchers have a pretty good handle on how freezing occurs. Melting, on the other hand, has proved far trickier to discern. But new findings are chipping away at the problem. In the current issue of Science, researchers report having observed premelting within a crystal for the first time. Previously, this stage had been seen only on crystal surfaces. Premelting, it appears, starts at defects in the crystalline structure, such as the cracks and grain boundaries among the otherwise orderly atoms. The image above shows a cross section of a crystal, with the circles representing spherical particles. The colors indicate the frequency of particle vibrational fluctuations as the crystal was heated. Premelting manifested as an increased movement along the defects in the crystal, and subsequently spread into the more ordered areas.