Number 19 (Story #3), January 29, 1991 by Phillip F. Schewe and Ben Stein FLUORESCENCE FROM SINGLE IMPURITY MOLECULES has been observed by scientists at IBM Almaden. Using a very thin (1-10 microns) crystal of the organic compound p-terphenyl cooled to 1.5 K and a laser with a very small spot size (5 microns), the fluorescence of individual impurity molecules (the organic molecule pentacene) could be monitored. The change in the molecule's spectrum over a period of minutes provided information about the impurity's local molecular environment. (Nature, 17 Jan. 1991. Contact W.E. Moerner, 408-927-2426.)