German physicist who discovered the ultraviolet region of the spectrum and thus helped broaden man's view beyond the narrow region of visible light to encompass the entire electromagnetic spectrum from the shortest gamma rays to the longest radio waves.

A pharmacist in Liegnitz, Silesia, from 1791 to 1795, Ritter studied medicine at the University of Jena, where he taught until he gained the patronage of the duke of Saxe–Gotha. In 1800, only months after the English chemist William Nicholson succeeded in decomposing water into hydrogen and oxygen by electrolysis, Ritter duplicated the experiment but arranged the electrodes so that he could collect the two gases separately. Soon thereafter he discovered the process of electroplating.

In 1801 Ritter made the startling discovery that silver chloride, which decomposes in the presence of light, is more rapidly decomposed when exposed to the invisible, theretofore unknown radiation beyond the violet end of the spectrum.

Ritter devoted most of his efforts to the study of electricity and electrochemistry. In 1801 he observed thermoelectric currents and anticipated the discovery of thermoelectricity by Thomas Johann Seebeck. Ritter invented the dry voltaic cell in 1802 and an electrical storage battery the following year.