Neils Finsen demonstrated that the most refractive solar rays, which he called chemical rays (i.e., blue, violet, and ultra violet radiation), as well as light rays originating from an electric or voltaic arc, have a stimulating effect on the tissues, also killing bacteria involved in skin infections. Through a series of experiments, Finsen had in part, perfected an existing therapy and in part, developed a new therapeutic method that received his name, Finsen's Method, for the treatment of skin affections, such as lupus vulgaris and psoriasis. This chemical rays method utilizes a hollow convex lens filled with an solution of copper sulphate that filter out the thermal radiation of the sun light, while converges the chemical rays at 50 cm from the skin. Another approach is the voltaic arc, which uses divergent light rays that are made parallel to each other when passing through two convex lenses. The...