Robert L. Fleischer earned a Ph.D. in physics from Harvard University in 1957. He served on the faculty of the Massachusetts Institute of Technology from 1956 to 1960 before moving to General Electric as a research physicist, where he pioneered the study and use of etched particle tracks for a wide variety of applications. Fleischer continues his research as a professor in the Department of Geology of Union College. Address: Department of Geology, Union College, F. W. Olin Center, Schenectady, NY. 12308. Internet: fleischr@union.edu