Hippolyte Fizeau was a French physicist born on September 23, 1819. He is best known for his pioneering work in the field of optics and for being one of the first to measure the speed of light. Fizeau's experiments in the 1840s used rotating mirrors to determine that light travels at approximately 299,792 kilometers per second. In addition to his work on light, Fizeau contributed to the development of the spectroscope and studied the interference of light waves. His research laid the groundwork for future scientists, including Albert Einstein, who further explored the nature of light and its properties.