[mclennan-dearle] spectrum OF THE MERCURY ARC 189 



position of each maximum as closely as possible. In the same region 

 as that investigated by Paschen/ the positions of nine lines were deter- 

 mined and these accorded fairly well with the wave-lengths given by 

 him. As was expected, in regions where the latter gives two or three 

 lines in close proximity, only one maximum, corresponding to the mean 

 wave-length was recorded in our measurements. Corresponding to 

 the new line observed by H. Lehmann^ at 1 -464^1, a maximum was 

 found which appeared to vary slightly from 1-46/i to 1-50/i. The 

 mean wave-length of all the readings taken on this line was 1 -483^1. 

 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^l. Close to the line 

 we also found two others at 1 -067^1 and 1-090/^ respectively. The 

 presence of these lines was evidently suspected by Coblentz and Geer^ 

 since they state that certain observations were repeated "to learn 

 whether another line exists between 1 • 06ju and 1-I2fx where the curve 

 is very asymmetrica:l." Their instruments, however, were not suffi- 

 ciently sensitive to detect these lines. Beyond 1 • 7fx only one line 

 was found which was at 3 • l/j.. This confirmed the doubtful indications 

 recorded by the above-named pair of investigators. This part of the 

 spectrum waî 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 inten- 

 sities 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 re- 

 corded in their communications. In the last column the frequencies 

 of all the lines are given, reduced to a vacuum. 



iPaschen, loc. cit. 

 ^Lehmann, loc. cit. 

 Coblentz and Geer. Phys. Rev. 16 p. 284, 1903. 



