PHOTOGRAPHY AND PHOTOMICROGRAPHY. I37 



directly on the substage mirror of the microscope, but 011 a sheet of ground glass 

 (it may be the focusing plate of the camera) placed in front of the mirror of the 

 microscope. The coarse adjustment of the microscope should not work too easil)', 

 or else the mere weight of the microscope tube may throw out the focus after it has 

 been secured and before the picture can be taken. The connection between camera 

 and microscope must be light-tight. In absence of a proper device (foot of stand 

 in fig. 24), light may be cut out by several folds of black velvet pinned close. The 

 stage of the microscope should also be protected from bright reflected light when 

 photographing by transmitted light. If there is a rigid connection between the 

 camera and the top of the microscope, or if the latter rests on the base of the former, 

 the focus is apt to be injured by slight jars incident to putting in the plate-holder 

 or drawing the slide. For this reason it is better to have them separate, and the 

 carrier and draw-slide should be scraped, sandpapered or filed, and waxed, soaped, 

 or vaselined, so as to work \'er}' smoothly. An entire day spent in accomplishing 

 this end should not be counted as wasted time. 



With large horizontal cameras (plate 5) the work-table and tlie bellows-table 

 must be leveled up accurately with reference to each other, sidewise as well as 

 vertically, and then must be bolted to the floor. The order of apparatus beginning 

 at the window is: mirror, condensing lens, alum-cell, light-filter (Zettnow's fluid),* 

 microscope, automatic shutter, front board of the camera, large black diaphragm in 

 middle part of bellows, ground glass of the camera. The newer styles have a screw- 

 device for elevating or lowering the camera and another for elevating or lowering 

 the microscope, or the optical bench. Dr. Novy has added to his Zeiss table a very 

 convenient de\-ice by means of which the services of an assistant are dispensed with, 

 one person behind the ground glass of the camera being able from this position to 

 move the slide in any direction desired. The cost of the attachment is about #15. 

 Beginning with the center of tlie mirror at the far end of the work-table or 

 beyond it, and ending with the center of the ground glass at the back of the camera, 

 all parts of the apparatus must be coder ed accurately, /. e.^ the light reflected from 

 the center of the mirror must pass in a straight line through the center of the con- 

 densing lens, Abbe condenser, objective, and e}'e-piece to the center of the ground 

 glass at the back of the camera, otherwise a first-class negative will not be obtained. 

 The Abbe condenser must also be at the right distance from the stage of the micro- 

 scope ; the image will then be on the center of tlie ground glass, circular, uniformly 

 lighted, and free from distortion and color fringes, if the optical parts are in proper 

 working order. The distance of the Abbe condenser varies, of course, with the 

 objective. The Planar lenses require special substage condensers, such as those 

 shown in fig. 122. When the centering is perfect all the rest is easy, or becomes 

 easy with a little experience. If sunlight is used, an automatic shutter should be 

 placed on the end of the camera next the microscope, so that accurately-timed short 

 exposures may be made. The sun's rays should pass through several inches of fluid 



*This is a mixture of copper nitrate and chromic acid in distilled water. It lets through only 

 the greenish-yellow rays. This fluid acts on the cement of the flint-glass container, and should 

 not therefore, be allowed to stand in it longer than necessary. The latter should then be washed 

 in pure water and properly drained. 



