Emission Spectrum of the Mercury Arc. 691 



line observed by H. Lehmann* at 1*464 /*, a maximum was 

 found which appeared to vary slightly from 1*46/1. to 1*50 //,. 

 The mean wave-length of all the readings taken on this line 

 was 1*483 fx. In addition to these, four other lines were 

 recorded, two of which had already been located by W. 

 Coblentz and W. C. Geer, with slightly higher values for 

 the wave-lengths. In their work a line is given at 1*045 /x, 

 while in ours it was found to be at 1*038 /i. Close to this 

 line we also found two others at 1*067 /i and 1*090 /jl respec- 

 tively. The presence of these lines was evidently suspected 

 by Coblentz and Geerf, since they state that certain obser- 

 vations were repeated "to learn whether another line exists 

 between 1*06 fi and 1'12/x where the curve is very asym- 

 metrical." Their instruments, however, were not sufficiently 

 sensitive to detect these lines. Beyond 1*7 ja only one line 

 was found, which was at 3*2 /x. This confirmed the doubtful 

 indications recorded by the above-named pair of investigators. 

 This part of the spectrum was not as thoroughly examined 

 as might be desired, and it is just possible that a closer 

 examination might have revealed other maxima, particularly 

 in the region of 3*7/*, where indications, as will be shown 

 below, point to the possible existence of a new line. 



In Table I., the wave-lengths of the lines isolated in the 

 present investigation are given in the first column and their 

 relative intensities in the second. Accompanying these are 

 given in order the wave-lengths of the lines determined by 

 other investigators, namely, Paschen, Lehmann, Moll, and 

 Coblentz and Geer. The intensities are given for the first 

 two, but in the case of the others no intensities are recorded 

 in their communications. In the last column the frequencies 

 of all the lines are given reduced to a vacuum. 



V. Discussion of Results. 



If the measurements made by the writers be compared 

 with the others given in Table I., it will be seen that the line 

 observed by us at 3*02 /z is probably the same as that given 

 by Coblentz and Geer at 3*00 /a, and the maximum at 1*72 /jl 

 doubtless corresponds to the group of four lines given by 

 Paschen between 1*692 jj, and 1*711 /a. There is no line 

 given by the others near 1*483 unless it be that given by 

 Paschen at 1*529 n and the one given by Moll at 1*52 /x. 

 The maximum noted at 1*377 //, represents probably a com- 

 bination of Paschen's two lines at 1*395 /jl and 1*367 /x, and 



* Lehmann, loc. cit. 



t Coblentz and Geer, Pbys. Rev. xvi. pp. -284, 903. 



