NO. 17 



ULTRA-VIOLET INTENSITIES McALISTER 



3,200 A. excluded). These wave-length limits are only approximate 

 because the filters do not have a sharp " cut-off." There is a region 

 of 200-300 A. in which the change from opaqueness to transparency 

 takes place. A typical change is seen in Table i, column 4, which is 



Table i. Instrumental constants 



the difference — transmission of fused quartz water cell minus the 

 transmission of the barium flint filter. A series of four diaphragms 

 was used to exclude radiation other than that coming directly from 

 the arc. The results of these measurements are given in Table 3. 

 They are compared with the summation of the monochromator 

 measurements and correlated with the measurements of other ob- 

 servers in the discussion. 



