TIIE CAMERA LUCIDA v. PHOTOGRAPHY.
The contrivance shown by Fig. 673 is the ordinary camera Nelda, or Beale's neutral tint reflector, consisting of a piece of smoked glass placed at an angle of 45°, while Fig. 674 shows a prism reflector. The magnified image of the object being pro jected upon a sheet of paper by reflection, it is a comparatively simple matter to pro can be rendered apparent, drawn or pho tographed, and thus kept in the form of permanent records. As the minute structures of various substances are often characteristic, the microscope is one of the most useful instruments of scientific research. The application of photo graphy to the delineation of microscopic objects dates back to the very early clays when the camera first came into use, but it is only within the last twenty years that it has taken the place it really deserves, and become something more than a scientific curiosity. Previous to this the magnified images of objects under the microscope were obtained by a species of tracing ; some form of reflector or •camera Nelda being placed over the eye duce a drawing or, more correctly speak ing, a tracing of it. When, however, the object contains a considerable amount of fine detail, the production of a tracing showing all the detail will be found very • difficult and probably impossible, even when a skilled draughtsman is employed ; hence, if two drawings be made by different persons they will be more or less different, and neither will represent exactly the original object. The fact is,
a certain amount of the detail is left out or modified, and a good deal is clue to the 6 personal element introduced. Hence, if drawings of any common object in books on microscopy be compared, it will be found that these drawings are often quite unlike each other, and only to a limited extent resemble that which they are in tended to represent. The outlines may be good, but the detail is generally poor and frequently altogether wanting. When, on the other hand, a photograph of an object is taken, it resembles the original in every respect, every line, every dot, and all the light and shade being faithfully repro duced. It is evident that for very ac curate work photomicrography is the only process really available, and it is only for certain purposes—for instance, when certain detail is to be made more promi nent and other detail cut clown or left out —that the method of tracing with the camera lucida can be used with any success. The factors essential to the produc tion of a photograph of an object magni fied by the microscope are: (a) an illu minant, (b) a microscope with a camera attached, and (c) a sensitive plate. As the apparatus is a special one, it will be necessary to consider it rather closely, which can be done at the same time as the methods are explained.