28 FORAMINIFERA 



volt "floodlight" bulb in an ordinary pliable gooseneck which can 

 be quickly bent to any desired position. 



In actual operation a table was built in across the end of the 

 "exposure room" of the laboratory, the centre of the top remov- 

 able with a second solid shelf below. In this lower part the 

 camera and microscope are placed, also the counter-light. On 

 the top at the left is the strong light as already noted. This 

 arrangement brings the top of the camera when extended low 

 enough so that focusing can be done from the floor. A medium 

 position is thus obtained obviating stooping to place the slides 

 in position and change the diaphragm, and also standing on a 

 higher level for focusing. 



When these factors already mentioned have become fixed, a 

 table of variant factors should be worked out. The intensity of 

 the strong light may be varied by focusing, and this will 

 greatly change the time of exposure. The greatest speed can be 

 obtained with the filament just out of focus on the slide. Each 

 new bulb will be found to vary, sometimes as much as fifty per 

 cent, and the intensity is apt to decrease with use. This factor 

 must be constantly checked. Specimens will require very differ- 

 ent exposures. White foraminifera of tropical reefs containing 

 chalk-white Miliolidae will need much less exposure than the 

 gray, dull material of much of the American Cretaceous, for 

 example. Length of exposure should be increased rather than 

 opening the iris diaphragm. 



The best results will be obtained from fairly slow plates, and 

 any good plate will give excellent results. The normal develop- 

 ment time for the plate should be taken as the base, and length 

 of exposure, intensity of light, etc., varied until the desired 

 sharpness of the developed plate results. Tank development 

 is used entirely. 



When good negatives are obtained, the next step is to get the 

 size best adapted to the purpose desired. In this work an East- 

 man auto-focus enlarging camera is used. With this camera 

 working in a vertical position no focusing is necessary, with the 

 enlarging paper placed directly on the table in the red light, 

 with a smaller auto-focus enlarger a magnification of 31/4 times 

 may be obtained, making the final print 60 to 75 diameters, a 

 size sufficient for all practical purposes. Where records are de- 

 sired for filing in the laboratory, printing is done on double 



