Beauty is truth, Keats declared, and truth beauty. Many prominent scientists have wished a version of this famous equation described their own work. The British quantum theorist Paul Dirac, for one, called his career “a search for pretty mathematics.” Most scientific aesthetes gaze fondly upon equations or arrangements of facts. A few, like the science writer George Johnson, also see beauty in the act of research. Johnson’s new book, “The Ten Most Beautiful Experiments,” is an appealing account of important scientific discoveries to which a variation of Keats applies: occasionally, beauty yields truth.