Gustav Kirchhoff

Gustav Kirchhoff (1824–1887) was a German physicist with a gift for turning messy tangles of wires into clean bookkeeping. He wrote down the two rules that let anyone solve a circuit — and he did it while still a student.

A mark on the subject

Every electronics engineer alive leans on Kirchhoff's laws: charge doesn't pile up, so everything flowing into a junction must flow out again; and voltage is like height, so around any loop the ups and downs must cancel to zero. Two simple bits of common sense — and together they crack circuits far too complicated to guess.

Kirchhoff's circuit laws are only half his story. Teaming up with the chemist Robert Bunsen (of burner fame), he noticed that each element glows with its own unique fingerprint of colours when heated. By spotting those same dark lines in sunlight, they worked out what the Sun is made of — without ever leaving the lab. When a banker sniffed that gold in the Sun was useless if you couldn't bring it back, Kirchhoff later collected his prize medal and dryly noted: "Here is gold from the Sun."