Book excerpt: A physics professor pairs short, elegantly written essays with simple drawings that offer engaging and accessible explanations of 51 key ideas in physics, from triangulation to relativity and beyond Humans have been trying to understand the physical universe since antiquity. Aristotle had one vision (the realm of the celestial spheres is perfect), and Einstein another (all motion is relativistic). Understandings often begin with a drawing, a humble but effective tool of the physicist's craft, part of the tradition of thinking, teaching, and learning passed down through the centuries. Don Lemons, a professor of physics and author of several physics books, pairs his essays with drawings that together convey important concepts from the history of physical science. The essays proceed chronologically, beginning with Thales' discovery of triangulation, the Pythagorean monochord, and Archimedes' explanation of balance. Readers will learn about Leonardo's description of “earthshine” (the ghostly glow between the horns of a crescent moon), Kepler's laws of planetary motion, and Newton's cradle (suspended steel balls demonstrating by their collisions that for every action there is always an equal and opposite reaction). Lemons reaches the 20th and 21st centuries with pieces on the photoelectric effect, the hydrogen atom, general relativity, the global greenhouse effect, Higgs boson, and more. The essays also place the science of the drawings in historical context—describing Galileo's conflict with the Roman Catholic Church over his teaching that the sun is the center of the universe, the link between the discovery of electrical phenomena and the romanticism of William Wordsworth, and the shadow cast by the Great War over Einstein's discovery of relativity.