In medicine as in other fields, photography finds its usefulness as a valuable adjunct to didactic teaching. It is an accurate and impartial portrayal of the object viewed.
The ether spectrum is arbitrarily divided. That portion of the spectrum which is visible lies between about 4,000 and 8,000 angstroms. Beyond the 4,000 angstrom level are the shorter rays: the ultraviolet, roentgen, gamma and cosmic rays, in the order given. The rays longer than the red (at 8,000 angstroms) are the infra-red rays (heat rays) and the hertzian rays, a portion of which has been utilized in radio broadcasting short wave and radio communication. There is no sharp definition between the rays but rather a gradual merging.
All photographic plates or films are more sensitive than the human eye in the ultraviolet area. They register from about 3,300 angstroms. The shortest wavelength that the eye perceives is 4,000 angstroms. The