120 



MICROSCOPIC TECHNIQUES 



2. Norberg Technique 



Apparatus 



A diagram of the optical system is given in Figure 12. For work in 

 the visible range, the light source employed is a 100 watt tungsten 

 band lamp (A) supplied with current from a large capacity (150- 

 200 amp. hr.) storage battery. Monochromatic light is obtained from 

 a Winkel-Zeiss monochromator (B) . (C is second monochromator 

 slit.) A filter (F) may be used between the condenser (E) of the 

 microscope and the sample slide (G) . The microscope objective is 

 indicated by H and the ocular by 0. During measurement the ocular 

 is removed and the light is reflected by the prism (/) , which is mov- 



Af L . 



/ 



h! 



H 





,.G 



^7 



KyE 



Fig. 12. Microphotometer. 

 From Norberg (1942) 



Fig. 13. Photocell amplifying circuit. 

 From Norberg (1942) 



able about both a horizontal and vertical axis, to the photocell (L). 

 Potassium cells are employed for wavelengths 450-550 m^u, and 

 potassium-cesium cells for longer wavelength. The current generated 

 in the photocells is amplified by circuits in M and then conducted to 

 the galvanometer (A^). Details of the amplifying circuit will be con- 

 sidered subsequently. 



For measurements in the ultraviolet region a high-pressure mer- 

 cury lamp (P) with movable prism (S) and 90° prism T, of the 

 Philips Philora H P 300 type, is used with a spectral filter {R) . 

 Variations in the intensity of the radiation from the mercury lamp 



