Developer unit having an indexable magnet

An apparatus in which a latent image is developed with magnetic developer material. A rotating applicator roll transports the developer material. A magnet is mounted rotatably interiorly of the applicator roll and generates a magnetic flux field which attracts the developer material to a portion of the surface of the applicator roll. The magnet rotates under the influence of the magnetic flux field force applied thereon. When the apparatus is developing the latent image, the magnet is prevented from rotating in a first position wherein the magnetic flux field attracts the developer material to the portion of the applicator roll adjacent the latent image. Conversely, when the apparatus is not developing the latent image, the magnet is prevented from rotating in a second position wherein the magnetic flux field attracts the developer material to the portion of the applicator roll spaced from the latent image. An apparatus of this type is particularly useful in color electrophotographic printing wherein successive electrostatic latent images are developed with different color developer materials. In a color printing machine, one color developer material is being developed on the latent image with the other color developer materials being spaced from the latent image to prevent intermingling of colors.