6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 87 



RESULTS AND DISCUSSION 



Using the double monochromator — with the entrant slit set at 

 0.05 mm and the middle slit 0.075 i^^"'' — a"<^I the vacuum thermocouple, 

 the high-intensity spectrum was mapped by taking readings one slit 

 width apart throughout. The arc was operated at 4.5 amperes and 

 an average of 143.5 volts. 



In the region 7,000 to 6,000 A. readings were taken every 50 A., 



6,000 to 5,000 A. " " " " 25 A.. 



5,000 to 4,000 A. " " " " 20 A., 



4,000 to 3,500 A. " " " " 10 A., 



3,500 to 2,500 A. " " " " 5 A., 



2,500 to 2,100 A. " " " " 2.5 A. 



Readings were also taken at the peaks of the maxima. This gave a 

 map of the spectrum of the highest resolution attainable with the 

 setup. Fifty maxima many of which are complex were observed. 

 Then a single monochromator was used with o.io-mm slit, and read- 

 ings were taken on 32 of the stronger lines. The intensities obtained 

 with the double monochromator were then corrected slightly where 

 necessary so that they agreed with the more accurate values obtained 

 with the single monochromator. The arc was then operated at low 

 intensity and observations were made with the single monochromator. 

 The galvanometer deflections were read with a telescope. These data 

 are given in Table 2. Columns 2 and 3 are the galvanometer deflec- 

 tions for the same arc run at high and low intensity respectively. 

 This arc had been used about 400 hours. These deflections were 

 reduced to absolute intensities by multiplying by 1.33 (microwatts 

 per cm" for i mm deflection) and dividing by the product of corre- 

 sponding values for the transmission of the monochromator and of 

 the thermocouple window given in Table i, columns 2 and 3. These 

 intensities are given in Table 2, columns 4 and 6, and are in micro- 

 watts per cm ^ for a distance of 250 mm from the center of the arc 

 and on the perpendicular bisector of a line from the cathode to 

 the mercury pool. The values in Table 2, columns 7 and 8, show the 

 amount of flux excluded by the barium flint and transmitted by the 

 fused quartz water cell. These values are obtained by multiplying 

 the absolute intensities in Table 2, columns 4 and 6, by corresponding 

 values in Table i, column 4. The sums at the bottom of columns 

 4, 6, 7, and 8 in Table 2 are for comparison with the filter observations. 

 The sum of the intensities of all the lines of wave length less than 

 and including A 3,130 is of interest, as it is this part of the radiation 

 from the mercury arc that is useful in curing rickets and produces 



