These fundamental principles have been discovered and applied in the past fifty years--in the memory of the living. They have revolutionized science in all its departments. Our textbooks on Chemistry, Light, Heat, Electricity and Sound have had to be entirely re-written; and in many other departments, notably in medicine and psychology, they have yet to be re-written. Our textbooks are in a transition state, each new one going a step farther, to make the change gradual from the old forms of belief to the new, so that even Tyndall's textbook on "Sound" is now so antedated, or antiquated, that it might have been written in darkest Africa before the pyramids were built, instead of twenty years ago. --This text refers to an alternate Paperback edition.