Calcium 
39 
ON SPECTRUM SERIES. 
Il. 
I" is well that I should indicate the basis of these | 
statements, and for this purpose I throw onthe screen | 
a very small part of the spectra of two or three different | 
substances in order that you may see the way in which 
the work has been done. Take the lowest horizon. 
There we are dealing with zinc, and you see the way in 
which the triplets have been picked out. The triplet in | 
each case, of course, supposing it is the remnant of a | 
fluting, has its central line nearer to one side of the triplet 
than the other. All the triplets in the zinc spectrum are 
perfectly symmetrical from that point of view. If we | 
take the upper spectrum—that of calcium—we find also 
that the triplets are formed in exactly the same way. We 
can quite understand the enormous labour which has 
been involved on the part of the inquirers I have named | 
in working out from the spectra of a great many sub- 
stances and from all the different regions of the spectrum, 
visible and photographic, these delicate triplets. In a 
Cadmium 
Zinc 
Nb 
Vik E 
[AvucusT 24, 1899 
was far more simple than that of any other chemical 
elements. A short time ago, however, Prof. Pickering, in 
his magnificent work on the stars, to which I have already 
had the opportunity of referring, discovered a second 
series of lines. Not long after, Prof. Rydberg suggested 
that one of the most important lines seen in a large group 
of stars really represented a line of the principal series 
of hydrogen. That conclusion has been generally ac- 
cepted, although the evidence is considered doubtful by 
some; so that we now assume that hydrogen has three 
series like helium and asterium, and we seem therefore 
to be on solid ground in one direction, at all events, 
in regard to some gases. We have another series 
of metals of low atomic weight, and which therefore 
chemically are supposed to represent a considerable 
simplicity; we find that in the case of lithium and 
sodium we also deal with three series, a principal 
series and two subordinate series. The series of lithium 
are just as beautiful in their rhythm as the other series 
to which I have referred. The same remark applies ex- 
| actly to sodium. 
Now, it has recently been found that 
+t Vie Soot ——! te me 4 t : 
ey = eT Te Gia 
Fic. 6.—Parts of the spectra of calcium,"cadmium and zinc showing the triplets. 
great many cases they do not represent the strongest 
lines, those most easily seen, and they want a great deal 
of looking for. 
I next pass on to some more general statements, which 
I am anxious to put before you for the reason that you 
will not find them stated in any literature that I am 
acquainted with ; the subject has really not been gener- 
ally discussed at all. 
Some substances have three series, as in the case of 
helium and asterium. There are others like them ; and 
the most remarkable case which I have to bring before 
you is that of hydrogen. We do not know the meaning 
of it yet, but it has to be taken into account in any con- 
sideration of these questions. Until a little time ago only 
one series was known in the spectrum of this gas, and it 
was thought that on that account the atom of hydrogen 
1 A 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. 
(Continued from p. 370.) 
NO. 1556, VOL. 60] 
sulphur and selenium also give us three series. We have 
a principal series and the first and second subordinates, 
but the suggestion of anything beyond these three is 
confined to one or two lines in each case. Next let us 
take another gas, and see what happens in the case of 
oxygen. Ile have six sertes, that is twice as many as we 
know of in hydrogen, helium, asterium, lithium, sodium, 
sulphur, and so on. I should say that so far as that goes 
we are in the same condition that we were some time ago 
when we imagined that the gas obtained from the mineral 
cleveite was really a single gas with six series. Very many 
arguments have been employed to show that that view is 
probably not an accurate one ; so that some are prepared 
to separate the cleveite gases at spark temperatures 
into two, calling one helium and the other asterium. 
That brings these two constituents of the cleveite gas 
then to the same platform as hydrogen with the recent 
developments, lithium, sodium, sulphur, &c. If we come 
to consider this extraordinary condition in the case of 
