On this day, February 26th, in 1848, the French physicist Hippolyte Fizeau conducted an experiment that measured the speed of light with remarkable accuracy. Fizeau used a beam of light to measure the speed at which it traveled through a spinning cogwheel, which had precisely spaced teeth. By timing how long it took for the light to pass through the gaps between the teeth as the wheel spun, Fizeau was able to calculate the speed of light to within 5% of the modern-day value. This experiment was a groundbreaking achievement in the field of optics and paved the way for future discoveries in the study of light and its properties.