SHEILA TERRY / SCIENCE PHOTO LIBRARY SHEILA TERRY / SCIENCE PHOTO LIBRARY
Christiaan Huygens (1629-1695), Dutch physicist and astronomer, experimenting with colliding balls. Huygens derived the laws of elastic collisions from this work. As well as this he was a proficient astronomer, grinding his own lenses and using them to study the Orion Nebula, craters and surface features on the Moon and Mars, and the rings of Saturn. He was the first to show that the rings were not attached to Saturn, but encircled it. He was also a founder of the wave theory of light, and used his theory to explain reflection and refraction. Illustration from Physique Populaire (1891), by E. Desbeaux.
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