# Translations:The speed of light/3/en

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Roemer reasoned that the time lag of 1000 s represents the additional time that it takes for light from Jupiter’s moon to travel the extra distance across the diameter of the earth’s orbit. Thus, Roemer was the first person to show that the velocity of light is finite. In 1676, Roemer announced his discovery at a lecture at the Académie des Sciences. Christiaan Huygens (1629–1695) wrote to Roemer on 16 September 1677, asking for more information. Roemer’s discovery was a godsend because the finiteness of the velocity of light is essential to the workings of Huygens’ principle. Using Roemer’s data, Huygens was the first person to determine the velocity of light. In other words, Huygens performed the calculation