Around 1913, Compton devised a demonstration method for the Earth's rotation. In 1918, Compton studies X-ray scattering. In 1922, Compton found that X-rays wavelength increases due to scattering of the radiant energy by "free electrons". Scattered quanta have less energy than the quanta of the original ray. The concept futhers the "particle" concept of electromagnetic radiation. Compton also developed the method for observing at the same instant individual scattered X-ray photons and the recoil electrons (developed with A. W. Simon). In Germany, W. Bothe and H. Geiger independently form a similar method.