194 THE ROYAL SOCIETY OF CANADA 



already noted, there would need to be a line at about 3 -70//. A line 

 in this position, however, was not observed in our investigation; but 

 as already mentioned this portion of the infra-red spectrum was not 

 examined as closely as the region of somewhat shorter wave-lengths. 



VI. Summary of Results. 



I. Thirteen lines have been recorded in the infra-red spectrum 

 of the mercury arc between the wave-lengths 1 • 00/z and 3 • 02//. 



II. The existence of the line near 1-04/t which was shown to 

 exist by Coblentz and Geer but which was not found by later in- 

 vestigators, was confirmed by the finding of a line at 1 • 038/z. 



III. The existence of at least one line with a wave-length longer 

 than 1 • 70/1 was proved by the discovery of a line at 3 • Olp., which was 

 also in confirmation of the work by Coblentz and Geer. 



IV. Three new lines were discovered in the infra-red spectrum 

 at 1-067//, 1-090// and 1-270//. 



V. It has been pointed out that the frequency differences for the 

 lines 1 • 038//, 1 - 270/( and 3 • 02// are the same as those which characterise 

 the triplets in the subordinate series for the mercury arc spectrum 

 given by 7 = 2, p — m, d and y = 2, p — m, s. It has also been sug- 

 gested that possibly the lines at l-09/£ and 1-367/j are the third and 

 second numbers of a similar triplet with its first number in the neigh- 

 bourhood of 3-70//. 



