CHAPTER XII. 

 PROGRESSIVE EXAMPLES. 



IT is proposed in this chapter to give a few examples of 

 operations for subjects presenting various degrees of difficulty ; 

 taking to start with the easiest class of object likely to be met 

 with, and attacking it with the simplest apparatus likely to be 

 required for any class of work. 



Example 1. A subject presenting only light-obstruction, with- 

 out very delicate marks or structure, and with just enough of 

 color to give actinic contrast, thin and flat ; to be photographed 

 with a low power to a magnification not exceeding 20 diame- 

 ters; no ocular nor condenser, direct illumination. Subject; 

 a good section of wood. Objective : two inches focus or lower 

 power. If an oil lamp provide the illumination the wick to 

 be turned " broadside on." 



Procedure : Having focused the object with objective and 

 ordinary ocular, arrange the object and light carefully so that 

 the whole field is evenly illuminated; attach the camera to 

 the microscope, the ocular being entirely removed. Proceed 

 to adjust the focus on the ground-glass of the camera ; for this 

 the microscope tube will require more or less racking in. In 

 such work as this there is danger of the tube cutting off part 

 of the field ; a good wide tube is therefore an advantage. 

 Notes : It is supposed that the reader has studied the foregoing 

 instructions and diagrams with regard to means for preventing 

 access of stray and reflected light to the sensitive plate. The 

 leather cap seen at No. 11, on Fig. 16, is in the writer's prac- 

 tice placed on the end of the tube, and the camera is then 

 pushed forward till the brass cap on the front passes into 

 the leather cap 11, thus forming a light-tight junction. 



In order to make sure that the lighting of the field is even, 

 the best plan is to remove the ground-glass of the camera, and 



