THE special theory of relativity was formulated by Albert Einstein twenty-two years ago. The general theory with its application to universal gravitation was published eleven years ago. The relativistic viewpoint has become an accepted principle and instrument in physical science. Yet a complete understanding of the ideas underlying it is comparatively rare among laymen, and far from being universal even among men of science. This is natural, since the theory of relativity presupposes a break with preconceived notions, hallowed by unquestioning acceptance at the hands of untold generations of experience and thought. We shall in this article consider a few of the difficulties that have come to the notice of the writer.