CH. Villi PHOTO-MICROGRAPHY 217 



that the screen should cut out much of the blue end of the spectrum and also 

 the special color transmitted by the object. 



Alcoholic solutions of the dye chosen may then be used to stain collodion 

 (see Ch. IX) or either alcoholic or aqueous solutions may be used for staining 

 glass plates coated with 20% to 30% gelatin. 



§ 294. Position and Exposure with Color-Screens. — It does not make 

 much difference where the color screen is placed provided no light reaches 

 the plate which has not passed through it. The most convenient position is 

 between the source of light and the object. If one uses a glass screen or 

 screens of stained collodion or gelatin on glass, the most convenient position 

 is in the holder for the central stop diaphragms just under the condenser. 



The length of exposure required when color screens are used is ordinarily 

 considerably increased. For color sensitive plates the increase is greatly 

 lessened if screen and plate are mutually adapted. 



PHOTOGRAPHING WITH A MICROSCOPE* 



I 295. The first picttires made on white paper and white leather, sensitized 

 by silver nitrate, were made by the aid of a solar microscope (1802). The 

 pictures were made by Wedgewood and Davy, and Davy says : "I have found 

 that images of small objects produced by means of the solar microscope may 

 be copied without difficulty on prepared' paper, "f 



^Considerable confusion exists as to the proper nomenclature of photography 

 with the microscope. In German and French the term micro-photography is 

 very common, while in English photo-micrography and micro-photography 

 mean different things. Thus: A photo-micrograph is a photograph of a small 

 or microscopic object usually made with a microscope and of sufficient size 

 for observation with the unaided eye; while a micro-photograph is a small or 

 microscopic photograph of an object, usually a large object, like a man or 

 woman and is designed to be looked at with a microscope. 



Dr. A. C. Mercer, in an article in the Proc. Amer, Micr. Soc. , 1886, p. 131, 

 says that Mr. George Shadbolt made this distinction. See the Liverpool and 

 Manchester Photographic Journal (now British Journal of Photography}, Aug. 

 15, 1858, p. 203; also Sutton's Photographic Notes, Vol. Ill, 1858, pp. 205-208. 

 On p. 208 of the last, Shadbolt's word "Photomicrography" appears. Dr. 

 Mercer puts the case very neatly" as follows: "A Photo-Micrograph is a 

 macroscopic photograph of a microscopic object; a micro-photograph is a 

 ■microscopic photograph of a macroscopic object. See also Medical News, Jan. 

 27, 1894, p. 108. 



f In a most interesting paper by A. C. Mercer on "The Indebtedness of 

 Photography to Microscopy," Photographic Times Almanac, 1887, it is shown 

 that : "To briefly recapitulate, photography is apparently somewhat indebted 

 to microscopy for the first fleeting pictures of Wedgewood and Davy [1802], 

 the first methods of producing permanent paper prints [Reede, 1837-1839], 

 the first offering of prints for sale, the first plates engraved after photographs 



