Emission Spectrum oj the Mercury Arc. 693 



in fig. 8, and others showing the new lines at 1-27 ft, 1*090/4, 

 and 1*067 ll are given in figs. 9 and 10. It will be noted 

 that the maxima at 1*27 ll and 3*02 ll are fairly sharp, while 

 those shown in fig. 10 are somewhat broader. 



A comparison o£ the intensities assigned to the various 

 lines by the different investigators affords an interesting- 

 study. Paschen says in his paper that he found the line at 

 1*014 ll was the most intense in the whole mercury spectrum, 

 and that on the same relative scale as that recorded in 

 Table L, he found the mercury green line at \ = 5461 A.U. 

 was represented by an intensity of 42, i. e., rather more than 

 one-half of the intensity of the line 1*014 ll. In the measure- 

 ments of the writers it was found that if the energy in the 

 line at 1*014//, be represented by 30, that in the line at 

 X=5461 A.U. was found to be represented by 40, or one- 

 third more than that of the line 1*014 /x. On looking at 

 Lehmann's results it will be seen that though there is no 

 value given for the intensity of the green line, that of the 

 line 1*015 ll is given by him as the weakest in the infra-red 

 spectrum. .This was probably due to the method of registering 

 the spectrum used by Lehmann, for it will be remembered 

 that by it the lines were recorded by their inverting action 

 on a phosphorescent screen. It is quite possible that the 

 line 1*015 /a, being nearer to the wave-lengths of the visible 

 spectrum than any of the others recorded, would not have 

 so strong an effect as waves of longer length. As regards 

 the relative intensities of the lines 1*014 ll and 5461 A.U., it 

 was noted by Paschen"* that if the vapour-pressure in his 

 lamp was increased, the relative intensity of the line 1*014 /a 

 came out still higher, while with a low vapour-pressure the 

 intensity of the tw r o lines was about equal. This may explain 

 the values of the intensities found for these lines in the 

 present investigation. 



In looking for series relationships among the lines given 

 in the first column of Table I., it was seen that the frequencv 

 differences for the lines 1*038 /*, 1*27 ll, and 3*02 yrx are prac- 

 tically the same as those which characterize the subordinate 

 series triplets in the mercury spectrum given by v = 2, 

 p — m, d, and v = 2, p — m, s. This will be evident from the 

 numbers given in Table J I. It will be noted, too, that the 

 frequency difference between the line given in our list at 

 1*09 ll and the one given by Paschen at 1*367 is equal to 

 1860*4, which approximates, as the table shows, to the 

 frequency difference between the second and third members 

 of the triplets of the two subordinate series mentioned above. 

 * Paschen, Ann, d. Phys. xxvii. 3. p. 559 (1908). 



