220 PHOTO-MICROGRAPHY \CH. VIII 



tween two cover-glasses is needed. By combining a little picric acid with the 

 solution or by the use of a thin piece of signal green glass only light between the 

 fixed lines E and F, is allowed to pass. This is not therefore so generally useful 

 as dichromate. 



(4) Bothamley's aurantia color screen is a saturated alcoholic solution of the 

 aurantia added to collodion of 3 to 4%. The collodion is poured on a large cover- 

 glass or a glass plate and allowed to dry. Pringle advises several screens of aurantia 

 of different shades. That is easily managed by adding a greater or less amount of 

 the solution to the collodion. This is a good screen and easily used. 



Petroleum light serves as a yellow color screen, and one can often get excel- 

 lent results with such a light when daylight or the electric light without a color 

 screen does not give a good picture. For all photography with the microscope 

 isochromatic or orthochromatic plates are advised. For many objects no color 

 screen is needed if one uses a petroleum lamp. 



$ 358. Position of the Screen. It does not make much difference where the 

 color screen is placed provided no light reaches the object which has not passed 

 through the screen. 



\ 359. Exposure with a Color Screen. The interposition of a color screen 

 increases the time of exposure from three to five times. One can learn the time 

 and whether or not to use a color screen, and the kind of a screen to use only by 

 experiment. To get the full benefit of these experiments for future work, every 

 negative should be carefully recorded (\ 360, table). It would also aid one materi- 

 ally, in the beginning at least, if he were to study the color screen used with the 

 micro-spectroscope and determine the wave lengths which are allowed to pass 

 through it (\ 195, 202). If this study were supplemented by a spectroscopic ex- 

 amination of the object to be photographed, one would learn to choose with great 

 accuracy the color screen which would give the best results. 



PHOTOGRAPHING WITH A MICROSCOPE* 



$ 361. The first pictures jnade on white paper and white leather, sensitized 

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



^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 dif- 

 ferent 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 Manches- 

 ter Photographic Journal (now British Journal of Photography} , Aug. 15, 1858, p. 

 203 ; also Button'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 macro- 

 scopic object. See also Medical News, Jan. 27, 1894, p. 108. 



