Henri Poincare´ is well known today for his contributions to many areas of mathematics and his popular writings on science. His attempts to apply physical theories to the evolution of the solar system and the rest of the universe are largely forgotten, except by a few specialists. Yet the crisp lucid prose of this brilliant thinker can still help the modern reader to appreciate the worldview of nineteenth‐century science, and provides a useful introduction to a fascinating historical phenomenon that I will call “the mathematician as naturalist” (see the box on page 44).