American physicist Albert Abraham Michelson (1852-1931) was interested in precise measurement, particularly of the velocity of light According to the theory current during the second half of the nineteenth century, light traveled in waves through an invisible and imponderable medium called "the ether," and there were several theories concerning how observations of the velocity of light might be affected by the movement of the Earth, which was thought to drag the ether along with it by gravity through its orbit Michelson believed that since the ether is at rest and the Earth moves through it, the speed of light as observed on the Earth's surface should depend on whether it is traveling in the same direction as the Earth's orbital motion or against it In 1881, while studying in the physics laboratory of Hermann von Helmholtz in Berlin, Michelson designed an instrument called the...