Who was the first person to give numerical value to the speed of light?

Answer 1

One of the earliest numerical values given for the speed of light (excluding Aristotle's 'infinite') would be that given by the 14th Century Indian scholar Sayana, given in his commentary on the Rigveda. Eerily enough, when converted to modern units, the value is remarkably close to the modern experimental value; this is probably a remarkable coincidence (see Subhash Kak, "The Speed of Light and Puranic Cosmology").

Probably the earliest published empirical value for the speed of light was obtained by Ole Christensen Romer in 1676. By observing the difference in time it took for the moons of Jupiter to orbit around the giant planet when it was closest to Earth, and when it was furthest from Earth. This gave an approximate value of 227 thousand kilometers per second, which is about 75% of the modern accepted value.

Answer 2

Back in the early 1600s, Isaac Beckman, a Dutch scientist, attempted to generically find out the speed of light in a somehow primitive and inaccurate experiment. Following him, a decade of so later, was Galileo, multi-majored scientist, who also proposed a relatively inefficient experiment, though two or three decades passed and some still applied his studies.

Later, in the later 1600s, the first approximate estimate of the said speed of light was made by Romer. He estimated that light would take around 25 minutes to sucessfully cross Earth's orbit diameter. Huygens, famous for his still-used theory, then approximated a value of 220,000 km/s for the speed of light.

Alber Einstein came as one to end this long debate, but did not attempt to find out the actual speed of light, but rather contradicted some earlier studies that suggested that speed of light is finite and vary according to mediums. Hence, his famous E = mc2 formula.

Years passed, and many scientists attempted to decrease the inaccuracy in the speed of light, until late 1900s, around 1973, a group of scientists game a definite value of 299,792,546 m/s, which was obviously different than previous experiments. Back-to-back experiments were implemented, and the speed of light was nailed down to 299,792,548 m/s, approximately equale to 3x108 m/s, which we now use in solving problems.