BAND OF AMMONIA, AND ITS OCCURRENCE IN THE SOLAR SPECTRUM. 359 
Birge has found a hyperbolic relation between d x and m in the case of cyanogen, 
but it does not seem that this is applicable to the series under consideration, with the 
possible exception of e and £ While it is possible to give approximate formulae of the 
usual type for these series over a large part of their ranges, there seems little hope at 
present of finding any accurate formula which can be adapted to all of them. One 
can hardly resist the conclusion that there is some connection between the groups of 
three and the central maxima, but no numerical relation has yet been established. 
Fig. 2. Curves representing the varying distances between successive lines in the series a to y. 
(The dotted portions of the curves are somewhat doubtful.) 
It should be noted that in addition to the main series formed from the groups of 
three, there are other fragmentary series of fainter lines having intervals between 
successive lines of the same order of magnitude as those of the main series. These are 
indicated in the general table by a', a", and S'. 
The Central Maxima .—'The series which constitute the central and secondary 
maxima,, so far as they have been identified, do not appear to present any unusual 
VOL. CCXVIII.-A. 3 B 
