Ehrenhaft adapted his apparatus to measure the elementary charge and subsequently became involved in a bitter controversy with Robert Millikan, claiming to have measured an electric charge less than that of a single electron, Millikan being passed over for the 1920 Nobel Prize in physics owing to the unresolved nature of the debate. Controversy eventually subsided as more and more physicists were swayed by Millikan's results but even as late as 1940, Albert Einstein wrote: