New series of lines in the spark spectrum of magnesium

A recent investigation suggested that the spectrum of hydrogen was unique in having two Principal series of lines which are related to each other in the same manner as Diffuse and Sharp series. One of these series begins with a line at λ 4686, and the other with a line at λ 3203, the two series converging to the limit 48764 on the frequency scale. The lines in question have so far only been produced by passing powerful discharges through helium tubes (which also contain hydrogen), but in accordance with the work of Rydberg, they have been attributed to hydrogen on the ground of their series relationship with lines known to be due to hydrogen. In seeking for further examples of such series, analogy with hydrogen suggested spark spectra as the most promising sources. One of the most remarkable spark lines is the well-known line of magnesium λ 4481, which is ordinarily not visible at all in the arc, but is by far the strongest line in the spark. Further, there is a series of single lines in the arc spectrum of magnesium, first identified as such by Rydberg, which it seemed might possibly be analogous to the Balmer series of hydrogen lines. Magnesium therefore appeared to be a very suitable element for investigation, but existing records of the spectrum were altogether inadequate for the purpose in view. There were, in fact, only two recorded lines which could possibly be connected in series with 4481; namely, the lines given by Exner and Haschek at 3106·5 and 2659·5. Other associated ultra-violet lines, however, have now been photographed, and it results that the spark lines form two series like those of hydrogen, 4481 being analogous to the first Principal line of hydrogen 4686.