History of Speed of Light

The speed of light in vacuum is a fundamental property of nature. Determination of the speed of light was great challenge for the scientist. Many attempts were made for its detection. In 1667 Galileo Galilee made an experiment. Two observers A and B were kept on two hilltops with lamps. The lamps were initially covered. Observer A uncovers the lamp thereby sending the light to B and B uncovers the next lamp when he saw the light from A. The time interval for the covering and uncovering the lamps was noted. Then the velocity of light is calculated as

C = 2x/t, where x = distance between two lamps

                                t = time noted

The earliest method failed as the time interval was very much small. This experiment failed and Galileo concluded that the speed of light is finite but very high.

                Danish astronomer Roemer in 1675 succeeded to determine the speed of light by recording the date and time of eclipse of one of Jupiter's satellite. The value was 2.3x10⁸ meter per second which was small then present value. The terrestrial method was performed by French physicist Fizeau in 1849 and this was improved by Foucault in 1869. It was further modified by Michelson in 1927. The speed of light was 2.997927x10⁸meter per second.

                It is interested to know that speed of light was already estimated in Vedic age by the Hindu philosopher.