C. STACY FRENCH 



53 



source is brighter than a tungsten lamp. We run the lamp on alter- 

 nating current and thereby get 120 light pulses per second. An image 

 of the lamp is focused on the slit of a monochromator by a spherical 

 mirror. The monochromator is usually set to isolate a total band width 

 of 10 m/x. Stray light is removed by filters. As shown in Fig. 1, a block 

 diagram of the apparatus, this incident light may be measured by 

 means of a thermopile in a sliding mount or may be allowed to fall 

 upon the sample. 



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Fig. 1. Block diagram of the apparatus for recording fluorescence spectra. 



Most of the fluorescent light given off by the sample escapes, but 

 some of it is caught by another curved mirror and sent into an ana- 

 lyzing monochromator, which also isolates 10 m^u,, total band width. 

 Behind this monochromator is a filter to remove reflected incident 

 light and one to give some correction for the wavelength sensitivity 

 of the photomultiplier tube. The electrical output of this photomulti- 

 plier tube is amplified and passed through an attenuator which is 

 linked to the wavelength drive of the analyzing monochromator by a 

 cam. The cam is cut to compensate for the variation of photomulti- 

 plier sensitivity with wavelength and also to include the varying 



