Austrian-born German chemist who devised and built an ultramicroscope in 1903. The microscope's illumination was placed at right angles to the axis. (In a conventional microscope the light source is placed parallel to the instrument's axis.) Zsigmondy's arrangement made it possible to observe particles with a diameter of one 10-millionth of a millimetre. He was awarded the Nobel Prize for Chemistry in 1925 for the elucidation of heterogeneity of colloids.