Why do we think matter is made of atoms and the Earth goes around the Sun? How big is the universe? Did it have a beginning or is it eternal? Is heat a fluid or just the random motion of molecules? Is light made of particles or is it a fluid or maybe something else? This book answers these questions and many more as it traces the development of the modern scientific understanding of the physical world. The historical approach allows us to see not only how the content of the physical sciences was formed but also how cultural, philosophical and religious influences and attitudes have played a major role in that development.