An instrument that uses a crystal to split X-rays according to energy, just as a prism splits visible light into the colours of the spectrum. It is named after the British physicist William Henry Bragg (1862–1942). The device has the highest resolution of any X-ray spectrometer, but suffers from low efficiency and can operate only in a very narrow band. It has been used to best effect in studies of the Sun, but has also been flown on X-ray satellites such as the Einstein Observatory.