1900: Ultraviolet Therapy
Ultraviolet therapy arose during the late nineteenth-century and early twentieth century to compliment the growing use of electrotherapy by using high-frequency electric current.
For deafness, it was believed to be beneficial in destroying bacterial growth, enhancing blood flow to the ear, and reducing any abnormal growths in the auditory canal.
Violet ray devices included an electrode that shone a bright glow when energized; the ray was believed to cure anything.