Measurement of the Speed of Light
Experimental measurements of the speed of light have been refined in progressively more accurate experiments since the seventeenth century. Until about 1850 the propagation of light was viewed in mechanical terms and it was presumed that it moved in a medium called the "luminiferous ether".
The first measurement of the speed of light is attributed to Danish astronomer Roemer. He measured systematic variations in the times at which the moons of Jupiter moved into the planet's shadow. Attributing these variations to different transit times for the light coming from Jupiter's orbit to the earth, he was able to calculate the speed of light.