KEPOBT OF THE SECRETABY 



133 



ULTEA-VIOLET 



The energy distribution in the mercury arc has been measured by 

 Doctor McAlister at a resolution 10 times greater than the previous 

 work. These results were presented at meetings of the Physical 

 Society. This work has been made possible through the loan of two 

 quartz monochromators by the Bausch & Lomb Optical Co. Figure 

 4 shows by the solid line the spectrum plotted with a single mono- 

 chromator; it is replotted with dotted lines where two monochrom- 

 ators are used, arranged so that the light passed first through one 



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 FitiunH 5. — Intensity record of mercury arc spectrum using double monochromator 



and then through the other. It will be seen that not only is the 

 background of energy observed between lines greatly reduced, but 

 also the lines are much narrowed, or, in other words, the resolution 

 is greatly increased. The intensities of the lines are only reduced 

 by a factor of two where the resolution and freedom from scattering 

 is increased by a larger factor. Figure 5 shows tlie spectrum plotted 

 with the double monochromator arrangement but a still narrower 

 slit. 



