NEGATIVE MAKING 6j 



this purpose I have chosen a slide of carci- 

 noma which may be of interest to all, and 

 certainly will be to the medical men among 

 them as an illustration of diseased tissues. A 

 low power, less than 100 diameters, shows its 

 details very well. I have, therefore, selected 

 a |-inch objective, which, with the Spencer 

 i-inch aplanatic ocular, gives just the desired 

 amplification with a moderate bellows exten- 

 sion. We will use acetylene this time from a 

 iVfoot burner as the radiant instead of the 

 Welsbach incandescent mantle, and you will 

 notice I have attached an achromatic condenser 

 to the substage of microscope. The specimen 

 is placed on the stage and the radiant (mounted 

 on a low movable stand like the Welsbach) is 

 made to occupy the same position as the latter 

 in our first experiment. Looking into the 

 eyepiece, the object is now brought to a 

 focus, the radiant being moved about until the 

 field is evenly illuminated, when the condenser 

 is racked forward or back until an image of 

 the flame is seen projected perpendicularly 

 across the field of view. If it is not in the 

 center the stand carrying the burner must be 

 moved about until it is so. We now have 

 both object and radiant in focus together, 

 really " critical" illumination which, however^ 



