Felix Ehrenhaft (24 April 1879 – 4 March 1952) was an Austrian physicist who contributed to atomic physics, to the measurement of electrical charges and to the optical properties of metal colloids.

Though Theodor Svedberg had made important demonstrations of Brownian motion in colloids, Ehrenhaft extended the work to make observations of particles of silver in air.

[3] 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.

He became professor of experimental physics at Vienna in 1920 and was known as a conscientious researcher and effective lecturer though single-minded to the point of absurdity.

A review of his life work can be found in the Austrian scientific journal "Acta physica Austriaca", and in the article by Rohatschek on photophoresis (see sources below).