586 DR J. HALM ON 
proceed towards the tail, so that finally only the double line series will survive. It is 
very probable that the interval between the double lines which in the above bands 
increases steadily, may in more extensive groups reach a maximum and then decrease 
again further towards the tail. Now the feature thus described seems indeed to agree 
closely with the phenomena observed in the Cyanogen-band according to Dr 
JuNcBLUTH. I may be allowed to quote the author’s own remarks on this important 
point, /.c., 241 :—‘‘ Following the series further, another peculiarity appears, which, 
strange to say, has not been heretofore observed, though it comes out distinctly in the 
first-order spectrum. The lines become gradually broader as they recede from the 
head, and each finally separates into two lines when it has reached a breadth of about 
0°07 tm. We have now double lines similar to those above and below the second 
head. As the series proceeds, the interval between components of the double lines — 
increases to 0°09-—0'1 t.m., and then decreases until the components unite again to 
form one line. The lines of all the observed series show this behaviour, so that in 
certain parts of the band structure, as for example above and below A 3700, we have 
only double lines.” He further remarks that this is “‘a noteworthy property and must 
be considered in forming any valid theory concerning the origin of spectra.” The most 
remarkable feature seems to me to be the coincidence of the centres of the lines in 
both series at the point where the second series begins. In consequence of this 
agreement the band changes from the single line to the double line type steadily, ze. 
without indication of an abrupt change in the positions of the lines, thus giving the 
impression of one continuous series. But in fact, as the Oxygen-bands show, the series 
consists of two separate branches. The reason why in the Oxygen-bands we see a 
marked discontinuity between the two series is obviously that the lines of the first 
series fade off too early, v.e. before the beginning of the second series. If the faint 
close doubles, which Mr Lesrer calls the continuation of the first series, were more 
prominent, the appearance of the Oxygen-bands would agree with that of the Cyanogen- 
band, though the intervals between the components are here too great to produce 
the impression of widened single lines by the coalescence of the four superimposed 
components. 
I think that this view explains sufficiently the peculiar behaviour of the lines 
pointed out by Dr Juncsiuru. It reveals also a hitherto unknown similarity in the 
structure of bands of different substances, which may have a bearing on the theoretical 
aspect of the problem. But what interests us most of all at present is the 
probability that the first part of the Cyanogen-series consisting of single lines differs 
essentially from the second part, the double-line series, just as the first series of the 
Oxygen-bands differs from the second. I am inclined to think that there is even a third 
branch containing the single lines near the tail, so that in fact each of the four series 
given by Dr JuncBLuTH consists of three distinct parts, each of which satisfies a 
different numerical form of the RypBeRG-THIELE equation. The correctness of this 
view may appear from the following tables, where the three branches of ‘Series L.,” 
