Galotype Camera, Lucida
End of visual spectrum Ultra red, or invisible rays
Bodies which have the power of transmitting heat rays are said to be diathemianous, those which do not possess this power, athermanous, or adiathermanous. Glass being highly adiather-manous, photographic lenses, unless they are pointed at the sun, allow but few heat rays to pass to the sensitive film. Rock salt, on the other hand, allows the heat rays to pass very freely, and lenses or prisms of this material are required in making experi-ments on the calorific rays, or radiant heat.
Calotype, or Talbotype. A process commonly named after its patentee, Fox Talbot, but called by him calotype (na\6s, beautiful). It is but little used now, excepting in a modified form for making enlargements, but interesting from its being the first paper negative process used. The following is a short resume of the process: - Stout paper, of an even surface and as grainless as possible, is brushed over with a solution of iodide of silver in iodide of potassium. It is, when partially dry, washed twice or three times in distilled water to remove the iodide of potassium and dried, and it can be kept for some little time in this state, as it is but faintly sensitive to light. When required for exposure it is brushed over with a solution of gallo-nitrate of silver or aceto-gallo-nitrate, and exposed wet; the exposure required for an open view is about six minutes. In all cases a faint image of sky-line should be apparent. The image is developed with a solution of gallo-nitrate of silver in excess of gallic acid. The negative is well washed, fixed in hypo, and washed and dried in the usual way, then waxed or oiled to render it translucent.
Cameo. Photographs to which, by means of dies and press, a slight convexity is given.
Camera, Lucida. A reflecting device, a piece of flat glass being the simplest form, by which the reflection of a scene is made to appear as if superimposed on a sheet of paper. It