Curious Effect or Violet Rays upon the Electric Telegraph.

Scientific American 43, 15.7.1848

It is not perhaps generally known, that it a ray of light of a violet color, enter through a window in the neighborhood of a telegraph needle, magnetism is immediately imparted. We understand that the scientific world is in­debted to Mrs Somerville for discovery of the fact that a magnet may be made by the agen­cy of a ray of violet, probably from the orbit of the fair experimenters own blue eyes, but in reality, Mrs. Somerville has succeeded inconverting a common sewing-needle, by a simple process into a magnet by the agency of a ray of violet. Professor Morse has also given attention to the subject. Finding that his telegraphic needles were frequently out of order, from the effect of particular rays of light, he placed before them, in order to neutralize it, a sheet of yellow glass, in front of the apparatus, which does not permit the violet rays to pass, and this he has foned to have the desired effect.