220 PHOTO-MICROGRAPHY \_CH. V1I1 



tweea two cover-glasses is needed. By combining a liltle 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 dichroinate. 



(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 orthochroniatic plates are advised. For many objects no color 

 screen is needed if one uses a petroleum lamp. 



<j 35S. 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. 



'i 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 ( i> 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 made 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, savs 

 that Mr. George Sbadboltmade this distinction. See the Liverpool and Manches- 

 ter Photographic Journal ( now British Journal of Photography), Aug. 15, 1S5S, p. 

 203 ; also Sutton's Photographic Notes, Vol III, 1858, pp. 205-208. On p. 208 of 

 the last, Shadbolt's word "Photomicrography" appears. Dr. Mercer puts the 

 case very neatly as follows : " k photo-micrograph is a macroscopic photograph of 

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

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



