1870s

---

1873

Irish telegraph operator Joseph May discovers that the action of light causes variations in electrical resistance on bars of selenium and that these variations are proportional to the intensity of the light. An electrical signal can thus be created from light.

1875-1880

Based on discoveries in the photoconductivity of selenium, theoretical models called a Telectroscope are presented for the exploration of the image. Notable among are those by American inventor, George R. Carey, and the French scientist Constantin Selencq. Both of them are based on a panel divided into a large number of photoelectric cells.

1878

William Crookes discovers the properties of cathode rays through the "Crookes Tube".