Julius Plücker was born in Germany and made important contributions to physics and analytic geometry.
In 1859, while professor of physics at Bonn University (he was also professor of maths there!), Plücker became the first person to describe what are now called cathode rays. He had come across them while working with Geissler tubes (glass tubes named after the glass-blower Geissler), when he noticed a faint column of fluorescence coming from the cathode. Moreover, he realised that he could focus this using a magnet. Without Plücker’s observations and discovery, we might not have television, as his work was vital for the development of the modern telly!
He also did important work in spectroscopy, when he suggested that the lines in the spectrum of an element were particular to that element. This had great implications for astronomy, as it meant that astronomers could tell from earth what proportions of elements astronomical bodies were composed of.
He also invented what we call line geometry, in which points are replaced by lines. Sadly, he died in 1868, just before completing a large work containing his results, although it was published posthumously by his pupil and assistant Klein.