Albert Einstein introduces the principle of equivalence of gravitation and inertia and uses it to predict the gravitational redshift
Editors. "Principles of equivalence of gravitation and inertia used to predict the gravitational redshift". The Literary Encyclopedia. First published 01 May 2009; last revised 30 November -1.
[http://www.litencyc.com/php/stopics.php?rec=true&UID=6408, accessed 21 April 2015.]