The great Scottish scientist James Clerk Maxwell wrote in 1874 to a colleague: “I saw conductivity of Selenium as affected by light. It is most sudden. Effect of a copper heater insensible. That of the sun great.”

Maxwell was among many European scientists intrigued by a behavior of selenium that had first been brought to the attention of the scientific community in an article by Willoughby Smith, published in the 1873 Journal of the Society of Telegraph Engineers. Smith, the chief electrician (electrical engineer) of the Gutta Percha Company, used selenium bars during the late 1860s in a device for detecting flaws in the transatlantic cable before submersion.