Selenium cell


Selenium cell


Astronomy, photometry


Wooden box measuring 10 cm x 8 cm x2.5 cm, flips open to expose selenium cell. Cell measures 3.0 cm by 5.0 cm. Stebbins described the Giltay selenium cells he and Brown used in the selenium photometer as “Two wires are wound close together in a double spiral about a flat insulator, and the spaces on one face are filled with selenium which has been properly sensitized.” A photograph of the Giltay cell was included in the 1911 article in Popular Astronomy, “The measurement of the light of stars with a selenium photometer with an application to the variation of Algol.”

The selenium cell photometer is historically significant and was used by Brown and Stebbins starting in 1907. Stebbins met Brown at a physics department open house where Brown ran a demonstration using a selenium cell to ring a bell. That apparatus, and selenium cells housed in a wooden case, are found for sale in Max Kohl catalogs .


Giltay of Delft, Holland


Replacement: Michael Svec donated in 2021 a selenium cell in a wooden box. The cell measures 3 cm x 5 cm and has approximately 18 wires per centimeter which is consistent with the Giltay cell’s that Stebbins bought and used from AB Porter in Chicago, in July 1907 for $20. Stebbins and Brown used at least two Giltay cells numbered 93 and 94. The original cells are lost. This replacement cell does have a resistance that decreases when exposed to light, so it is function.


Circa 1910




physical object


University of Illinois Observatory, Urbana, IL


Selenium cell in wooden box
Historic picture of selenium cell



Giltay of Delft, Holland , “Selenium cell,” University of Illinois Observatory Collection, accessed February 21, 2024,