German physicist known for his work on electrical phenomena in gases and on cathode rays; he is also credited with discovering canal rays.

Goldstein studied at the University of Breslau (now in Wrocław, Pol.), where he received his doctorate in 1881. His career was spent at the Potsdam Observatory. He was primarily interested in electrical discharges in moderate to high vacuums. In 1886 he discovered what he termed Kanalstrahlen, or canal rays, also called positive rays; these are positively charged ions that are accelerated toward and through a perforated cathode in an evacuated tube. He also contributed greatly to the study of cathode rays; in 1876 he showed that these rays could cast sharp shadows, and that they were emitted perpendicular to the cathode surface. This discovery led to the design of concave cathodes to produce concentrated or focused rays, which became fundamental to numerous experiments.