368 
NATURE 
[AuGUST 17, 1899 
ON SPECTRUM SERIES. 
E have now, I trust, obtained a general idea of inor- 
ganic evolution so far as stratigraphic geology is 
concerned. You may remember that I pointed out that 
upon the various vegetable and animal forms which had 
been found in the various strata of the earth’s crust from 
the pre-Laurentian up to the Recent times, but that the 
science of embryology had also been brought into play, 
and that a succession of forms in the individual was 
there to attest the general line of descent. To-night we 
have to deal with the spectroscope and the motions of the 
smallest units of inorganic matter which we can get at, 
and to compare the results obtained in this way with 
some of those that the biologist has arrived at by means | 
of the microscopic examination of the smallest unit forms 
| 
the evidence for organic evolution not only depended 
_ the mineral cleveite to the action of an electric current. 
We observe that all rhythm has gone, and there seems 
to be a very irregular distribution ; but when we come 
to sort those lines out into series, we find that there is 
just the same exquisite order that we get in the case of 
the flutings. You notice in the photograph all the lines 
higgledy-piggledy, the next photograph will show that 
they have all been resolved into two sets of three series 
which very much resemble those that we saw before ; 
that is to say, they gradually get nearer together towards 
the violet, and they all get stronger towards the red. We 
have then two constituents of the cleveite gases, asterium 
and helium, and we find that their irregular line spectra 
when analysed into these series are translated into a 
wonderful order. I suggested many years ago that the 
lines in the ordinary line spectrum of a substance may 
really be remnants of compound flutings, and such in- 
Fic. r.—Compound flutings of carbon. 
that he can observe. From the spectrum point of view, 
this inquiry is included in the word “series.” In the 
study of series of lines in different spectra, we are on the | 
same ground plan as the biologist is when he is studying 
what he calls cytology, or the laws of cells. 
To explain what is meant by “series” I will refer to one 
or two photographs of what are termed fluted spectra. 
You will observe that such a spectrum is_ perfectly 
rhythmic from end toend. The whole of a fluting may | 
be regarded as a unit ; it is generally strongest towards 
the right or the red end of the spectrum, its elements 
gradually becoming dimmer as we approach the violet 
end. But a fluting is generally more than this ; it is 
built up of subsidiary flutings. Each of the subdivisions 
of it is in itself an almost exact representation in the 
small of what the whole thing is in the great; so that 
we have the conceptions of a simple fluting and a com- 
pound fluting. The compound flutinys are well repre- 
quiries as those that I have to refer to to-night really 
seem to justify that suggestion. Very well, then, we 
arrive at the fact that the term “ series” is one employed 
to related lines. It is impossible to suppose that these 
wonderful rhythmic series of lines are not related in 
some way to each other, and that being so we have to 
study their wave-lengths, that is, their positions in the 
case of any one element ; and not only so, but to see 
if any relation exists between the lines of different 
elements. 
The history of this quite modern inquiry is not very 
long, but short as it is | only propose to refer to it in the 
briefest possible manner. 
The first attempt to discover regularities in the lines of 
spectra was made by Lecoq de Boisbaudran,? who in- 
vestigated the spectrum of nitrogen. The conclusions 
he arrived at suggested that the luminiferous vibrations 
of the molecules could be compared with the laws of 
Fic. 2.—Simple flutings of nitrogen. 
sented in the flutings of carbon. It is by means of such 
photographs that t he existence of carbon in the sun has 
been determined. Each of the finer lines in one of the 
first elements of the compound fluting has a dark line 
corresponding with it among the Fraunhofer lines. In | 
the case of the spectrum of nitrogen we get the same 
exquisite rhythm, the same intensification of the series of 
lines towards the red, and the same division of some of 
the larger flutings into smaller divisions ; so that, as I 
said before, we have to consider flutings really as com- 
pound and not as simple phenomena. When we leave | 
these flutings and study an ordinary line spectrum, ina | 
great many cases all rhythm seems to have disappeared. | 
There is apparently no law and no order. Let us take | 
the lines seen when we expose the gases obtained from 
| 
4 Lecture to Working Men delivered at the Museum of Practical | 
Geology, on May 1, by Prof. Sir Norman Lockyer, K.C.B , F.R.S. { 
NO. 155 5, VOL. 60] 
sound, but as these were not based on wave-length de- 
terminations of sufficient accuracy, and also were not 
confirmed by Thalén, no great weight could be attached 
to the result. 
Stoney,® who followed up these investigations, was 
more successful ; he showed that the hydrogen lines C, F, 
and # were connected by the relationship 20: 27 : 32. 
Several other workers—Reynolds, Soret, &c.—took 
the subject up, but it was left for the more thorough 
work of Schuster4 to show that this theory could no 
1 Tt has always been customary with me in reproducing spectra in the 
form of illustrations to show the red end of the spectrum on the right hand 
side and the violet end on the left. As most of the workers on ‘‘series”’ 
have adopted the opposite way, I propose 7” ths /ectuve to depart from my 
usual custom and place the red in series spectra on the left, so that all the 
series illustrations may be comparable zxter se. 
2 Comptes rendus (1869), 69, 694- 
3 Phil. Mag., 1871 [4], 41, 201. 
4 Brit. Assoc. Report, 1880; Proc. R.S. (1881), 31, 337. 
