VISIBLE AND U.V. ABSORPTION HISTOSPECTROSCOPY 



115 



to 230 mix. However, since variations both in voltage and water pres- 

 sure affect the mercury lamp, the tungsten is employed for the 

 longerwave ultraviolet range. The spark source is used for wave- 

 lengths shorter than 235 m/i,. 



The radiation, after passing through a monochromator (C) is 

 concentrated on the object (/) on a quartz slide by the condenser 

 (//). (The second monochromator slit is at D, lens at E, and a 90° 

 ciuartz prism at F.) For ultraviolet work a fused quartz condenser 

 is used, and in the visible range a good achromatic type is employed. 

 Zeiss objectives designed for the longer ultraviolet (down to about 

 340 mju) or the fused quartz objectives of Kohler and von Rohr for 

 the shorter wavelengths are used (K) . For routine work down to 



V^ 



i^ o 



Fig. 9. Arrangement of Caspersson's apparatus 



for photoelectric absorption histospectroscopy. 



From Caspersson (1940) 



240 m/A, Caspersson ( 1940) found it convenient to have a glycerin 

 immersion lens corrected for 257 m/x with an aperture of 1.25, one 

 corrected for 275 m^a, and a long-wave ultraviolet recorrected 

 apochromat. Oculars with iris diaphragms (L) were employed. The 

 lenses in them were of quartz for the ultraviolet work. 



A 90° quartz prism (M), adjustable by means of micrometer 

 screws, is used to deflect the radiation through the opening of an 

 electrically driven rotating sector (A^) on to a photoelectric cell 

 (R). The prism can be replaced either by a Kohler focuser (Y) or 



