Today is the birthday of Hans Geiger, born in 1882, a German physicist known for the techniques he developed for detecting and counting charged particles. Geiger investigated the charge and nature of alpha particles and devised techniques for counting them. In 1925 Geiger and his colleague Walther Muller came up with a device, which was designed to be compact and portable and to measure alpha, beta, and other types of radiation. By 1928 the Geiger-Muller counter was being produced and used in radiation research labs. After noting that counters in separate rooms periodically picked up simultaneous bursts of radiation--the first detection of cosmic ray showers--Geiger became interested in studying cosmic radiation. In 1937 he and his colleague Otto Zeiller arrayed nine counters in a circle to determine the angular distribution of a cosmic ray shower.
[Source: Charles Coulston Gillespie, Ed. Dictionary of Scientific Biography. Charles Scribner's Sons, New York. 1973.]