"In 1880 Michelson was at Berlin in the laboratory of Helmholtz. There he started the experiment, which was later completed at Cleveland in collaboration with Professor E. W. Morley, of attempting to measure the motion of the earth with respect to the ether. Astronomers had found that the sun with its retinue of planets is moving toward the stars in the constellation Hercules at the rate of twelve miles per second, or four hundred million miles per year. This would be the motion of the sun if the stars were at rest, but as they are not at rest, the real problem of determining the motion of the sun remained unsolved. Michelson undertook to measure the motion of the sun with respect to that all-pervading medium, known as ether, which fills interstellar space."