Throughout the history of science, different thinkers, philosophers and scientists postulated the existence of entities that, in spite of their not being visible or detectable in their time, or perhaps ever, were nevertheless useful to explain the real world. We started this book by looking at a handful of these entities. These included phlogiston to account for fire; the luminiferous ether for propagation of radiation; the homunculus to provide for heredity; and crystalline spheres to carry the wandering planets around the earth. Many of these erroneous beliefs had held up progress, just as...

Throughout the history of science, different thinkers, philosophers and scientists postulated the existence of entities that, in spite of their not being visible or detectable in their time, or perhaps ever, were nevertheless useful to explain the real world. We started this book by looking at a handful of these entities. These included phlogiston to account for fire; the luminiferous ether for propagation of radiation; the homunculus to provide for heredity; and crystalline spheres to carry the wandering planets around the earth. Many of these erroneous beliefs had held up progress, just as...