For 40 years, Martin Perl plumbed the mysteries of matter. His experiments at the Stanford Linear Accelerator Center led to the discovery of the "tau lepton," a particle similar to an electron but vastly heavier, that plays a central role in one of the most fundamental questions in physics: "What is mass, and why do things have the masses they do?" This landmark contribution to science earned him the 1995 Nobel Prize in Physics. The son of Russian immigrants, he grew up in Brooklyn, New York. As a child, he loved reading, particularly mathematics and science, but a career as a...