Relativity: The Special and General Theory
Albert Einstein's Relativity: The Special and General Theory (1916; Robert W. Lawson's English translation, 1920) is Einstein's own popular exposition of the two theories that overturned classical physics. Written 'for those readers who, from a general scientific and philosophical point of view, are interested in the theory, but who are not conversant with the mathematical apparatus,' it explains the special theory's union of space and time and the relativity of simultaneity, then the general theory's account of gravitation as the curvature of spacetime, closing with reflections on the structure of the universe as a whole.
Translation
Robert W. Lawson (1920)