Fune 17, 1886] 
I will first take the earths which give absorption-spectra when 
their solutions are examined by transmitted light. These occur 
chiefly at the higher end, beginning with didymium and proceed- 
ing, through samarium, holmium, &c., to erbium, which is one 
of the least basic. The earths which give phosphorescent spectra 
chiefly occur at the lower end, but each group overlaps the other ; 
for instance, yttria occurs above erbia. 
One of the highest of the absorption-spectrum earths is 
didymia, The spectrum of didymium, as generally met with, is 
well known, and is given in my paper on “Radiant Matter 
Spectroscopy: Part 2, Samarium ” (par. 135). 
It has long been suspected that didymium is not a simple body, 
and in June 1885 Dr. C. Auer announced that by a series of 
many hundred fractional crystallisations he had succeeded in 
splitting up didymium into two new elements, one giving leek- 
green salts and the other rose-red salts. The green body he 
called Praseodymium and the rose-red Neodymium. I have not 
found that my method of fractionation gives a decomposition 
similar to this ; probably didymium will be found to split up in 
more than one direction, according to the method adopted ; but 
by pushing the fractionations at the didymium end of the series 
to a considerable extent, a change gradually comes over the 
spectrum. At the lower end the earth gives an absorption- 
spectrum such as is usually attributed to didymium, but with no 
trace of some of the bands in the blue end, the one at A 443 
being especially noticeable by its absence. The intermediate 
earths give the old didymium spectrum, the relative intensities of 
some of the bands varying according to the position of the earth 
in the series, the band 443 becoming visible as the higher end is 
approached. The highest fractions of all give the band 443 one 
of the most prominent in the spectrum, being accompanied by 
other fainter bands which are absent in the lowest didymium 
spectrum. 
I now come to a branch of the subject which promises to 
yield results even more fruitful than those given by the examina- 
tion of absorption-spectra : I refer to the spectra yielded by some 
of the earths when phosphoresced zz vacuo. This method 
has been so fully explained before the Royal Society, in my 
papers on ‘‘ Radiant Matter Spectroscopy,” that I need not 
repeat it. 
In my Bakerian Lecture on Yttrium (PAz/. Trans., Part 3, 
1885) I described the phosphorescent spectrum of this earth, and 
gave a drawing of it. In the Samarium paper I gave a similar 
description and drawing of the samarium spectrum, and also 
described and illustrated some anomalous results obtained when 
yttria and samaria were mixed together. Under the conditions 
described in the paper a sharp and brilliant orange line made its 
appearance, which at that time seemed as if it belonged to the 
samarium spectrum, and was only developed in greater intensity 
by the presence of yttria. This explanation, however, did not 
satisfy me, and I called the line (a 609 = 2693) “the 
anomalous line,” intending to return to it at the first opportunity. 
T have since further investigated the occurrence of this line, with 
more than usual good fortune in the extent and importance of the 
new facts thereby disclosed. 
Systematic fractionation was carried on with the portions of 
the general series giving the strongest appearance of line 609, 
an | it soon became apparent that the line closely followed 
sani arium. The presence of yttria was not necessary to bring it 
out, although by deadening the brightness of the other bands it 
was useful, not seeming to affect the line 609. Several circum- 
stances, however, tended to show that although line 609 accom- 
panied samarium with the utmost pertinacity, it was not so integral 
a part of its spectrum as the other red, green, and orange lines. 
For instance, the chemical as well as physical behaviour of these 
line-forming bodies was different. On closely comparing the 
spectra of specimens of samaria from different sources, line 609 
varied much in intensity, in some cases being strong and in 
others almost absent. The addition of yttria was found to greatly 
deaden the red, orange, and green lines of samarium, while yttria 
had little or no effect on the line 609 ; again, a little lime entirely 
suppressed line 609, while it brought out the samarium lines with 
increased vigour. Finally attempts to separate line 609 from 
samarium, and those portions of the samarskite earths in which 
it chiefly concentrated, resulted in sufficient success to show me 
that, given time enough and an almost inexhaustible supply of 
material, a separation would not be difficult. 
But what was then practically impossible to me, restricted with 
NATURE 
161 
limited time and means, Nature has succeeded in effecting in the 
most perfect manner. I had been working on samarskite, and 
many observations had led me to think that the proportion of 
band-forming constituents varied slightly in the same earth from 
different minerals. Amongst others, gadolinite showed indica- 
tions of such a differentiation, and therefore I continued the work 
on this mineral. Very few fractionations were necessary to show 
that the body giving line 609 was not present in the gadolinite 
earths, no admixtures of yttria and samaria from this source 
giving a trace of it. It follows, therefore, that the body whose 
phosphorescent spectrum gives line 609 occurs in samarskite, but 
not in gadolinite ; thus it cannot be due to samarium, yttrium, 
or a mixture of these two elements; the only other probable 
alternative is that the source of this line is a new element. 
Chemical fractionation is very similar to the formation of a 
spectrum with a very wide slit anda succession of shallow prisms. 
The centre portion remains unchanged for a long time, and the 
only approach to purity at first will be at the two ends, while a 
considerable series of operations is needed to produce an 
appreciable change in the centre, 
During the later fractionations of the gadolinite earths another 
set of facts, formerly only suspected, have assumed consistent 
form. The spectrum bands which hitherto I had thought belonged 
to yttria soon began to vary in intensity among themselves, and 
continued fractionating increased the differences first observed. 
It would exceed the limits of a preliminary note were I to enter 
into details respecting the chemical and physical reasons which 
lead me to the definite conclusions I now bring before this Society. 
More than 2000 fractionations have been performed to settle this 
single point. I will content myself with stating the results. The 
earth hitherto called yttria appears to be a highly complex body, 
capable of being dissociated into several simpler substances, each 
of which gives a phosphorescent spectrum of great simplicity, 
consisting for the most part of only one line. 
Taking the constituents in order of approximate basicity (the 
chemical analogue of refrangibility) the lowest earthy constituent 
gives a violet band (A 456), which I have reason to believe belongs 
to ytterbia. Next comes a deep blue band (A 482); then the 
strong citron band (A 574), which has increased in sharpness till 
it deserves to be called a line ; then come a close pair of greenish- 
blue lines (A 549 and A 541, mean 545) ; then ared band (A 619), 
then a deep red band (A 647), next a yellow band (A 597), then 
another green line (A 564) ; this (in samarskite yttria) is followed 
by the orange line (A 609) of which I have already spoken ; and 
finally, the three samarium bands remain at the highest part of 
the series. These for the present I do not touch, having my hands 
fully occupied with the more easily resolvable earths. 
In the Comptes rendus for April 19, 1886, M. de Boisbau- 
dran announced to the Academy that M. de Marignac, the 
discoverer of Ya, had selected for it the name Gadolinium. In 
February last I gave a short note on the earth Ya (Proc. Roy. 
Soc., No. 243, February 1886, and NATURE, vol. xxxiii., p. 525) 
in which I described its phosphorescent spectrum (agreeing 
exactly with that given by Ya of M. de Marignac’s preparation). 
Referring to my paper it will be seen that Ya is composed of the 
following band-forming bodies :—(451), (549), (564), (597), (609), 
(619), together with a little samarium. Calling the samarium 
an impurity, it is thus seen that gadolinium is composed of at 
least four simpler bodies. The pair of green lines (A 541 and 
2.549, mean 545), being the strongest feature in its spectrum,may 
be taken as characteristic of gadolinium: the other lines are due 
to other bodies. 
A hitherto unrecognised band in the spectrum by absorption 
or phosphorescence is not of itself definite proof of a new ele- 
ment, but if it is supported by chemical facts such as I have 
brought forward there is sufficient prima facie evidence that a 
new element is present. Until, however, the new earths are 
separated in sufficient purity to enable their atomic weights to be 
approximately determined, and their chemical and physical 
properties observed, I think it is more prudent to regard them as 
elements on probation. I should therefore prefer to designate 
them provisionally by the mean wave-length of the dominant 
band. In this I am following the plan adopted by astronomers 
in naming the minor planets, which are known by a number 
encircled bya line. If, however, for the sake of easier discussion 
among chemists a definite name is thought more convenient, I 
will follow the plan frequently adopted in such cases, and pro- 
visionally name these bodies as shown in the following 
table :— 
