Whether it is true or not that not more than twelve persons in all the world are able to understand Einstein's Theory, it is nevertheless a fact that there is a constant demand for information about this much debated topic of relativity. The books published on the subject are so technical that only a person trained in pure physics and higher mathematics is able to fully understand them. In order to make a popular explanation of this far reaching theory available, the present book is published. Professor Lorentz is credited by Einstein with sharing the development of his theory. He is doubtless better able than any other man except the author himself to explain this scientific discovery.