PHOTOMICROGRAPHY AND TECHNICAL MICROSCOPY 



791 



Electrical System. — The details of the electrical system are shown in Fig. 19. The 

 assembly of the apparatus as illustrated in Fig. 20 has been arranged to protect the 

 user against accidental electric shock and from exposure to short-wavelength ultra- 

 violet light. These short waves have an injurious effect on the skin, producing pre- 

 mature aging and small tumorous growths. If the spark-generating apparatus is not 



Fig. 20. — The ultraviolet microscope. 



shielded, long-continued exposure may result in serious injury to the operator. The 

 hands especially are exposed to the radiations when adjusting the spark, and some 

 frequent adjustment is required; the spark source is covered with a housing. A flexible 

 shaft provides a means for controlling the electrode. The housing must be ventilated 

 by an exhaust fan to prevent the fumes generated by the spark from contaminating the 

 atmosphere within and absorbing the ultraviolet liglit. 



Table II. — Monochromatic Objectives Corrected for X 



Tube Length 



275 Mm and 160-mm 



System 



Focal length /, 

 mm. 



N.A. 



Relative 



resolving 



power 



Dry 



Dry 



Glycerin . . 

 Immersion 



16 

 6 



2.5 

 1.7 



0.20 

 0.35 

 0.85 

 1.25 



0.40 

 0.70 

 1.70 

 2.50 



