This is one of a collection of phototubes from the University of Wisconsin that represents the efforts of the staff of the Department of Astronomy there, led by Joel Stebbins, to develop photoelectric sensor technology for astronomy in the first half of the 20th century. By the time commercial photodiode tubes of the sensitivity required for astronomy were available on the market, Joel Stebbins and Albert Whitford had already been using unique tubes fabricated by Jakob Kunz at Illinois for 25 years. Cells like this Continental Electric Co. CE-25 did not make the grade at first, but after the Second World War, their cathode formulations became good enough to produce the occasional cell useful to astronomers. Because the manufacturers could not reliably produce cells of great sensitivity, astronomers would work out arrangements whereby they would receive large lots of cells, test them to find the extra sensitive ones, and return the rest, purchasing only those tubes valuable for observations. Continental Electric's cells were some of the first commercially produced photoemissive cells to deliver sensitivities and dark currents good enough for astronomical observation and in doing so greatly broadened the accessibility of photoemissive observation previously constrained by the very small number of Kunz tubes which existed. CE-25s were used to make observations in the six-color photometer at Lick Observatory in the late 1940s. The University of Wisconsin donated this set of objects to the Museum in 2017.