This is the full text of James Jeans's Rouse Ball Lecture given in 1925 at Cambridge University, and surveys the field of atomic and subatomic physics.This is the full text of James Jeans's Rouse Ball Lecture given in 1925 at Cambridge University, and surveys the field of atomic and subatomic physics in the early days of quantum mechanics, with a brief historical perspective on measurement.This is the full text of James Jeans's Rouse Ball Lecture given in 1925 at Cambridge University, and surveys the field of atomic and subatomic physics in the early days of quantum mechanics, with a brief historical perspective on measurement.This is the full text of James Jeans's Rouse Ball Lecture given in 1925 at Cambridge University, and surveys the field of atomic and subatomic physics in the early days of quantum mechanics, with a brief historical perspective on measurement.The Rouse Ball Lecture, delivered on May 11, 1925.