[Marcu 10, 1923. 

322 NATURE 
: scopically in their preparations were zirconium and 
Letters to the Editor. titanium, It is interesting to notice that some of 
[The Editor does not hold himself responsible for the most prominent hafnium lines have been present 
opinions expressed by his correspondents. Neither 
can he undertake to return, nor to correspond with 
the writers of, rejected manuscripis intended for 
this or any other part of NATURE. No notice is 
taken of anonymous communications. | 
The Optical Spectrum of Hafnium. 
DurinG the progress of the work of Coster and 
Hevesy on the concentration and isolation of the 
new element hafnium (atomic number 72), the dis- 
covery of which was announced in Nature of 
January 20, p. 79, we have examined spectroscopically 
a large number of their preparations in order to 
establish the optical spectrum of hafnium, and at 
the same time to assist in the chemical work on its 
isolation. In all our exposures we have for the 
sake of comparison also photographed the spectrum 
of a specimen of very pure zirconium prepared by 
Coster and Hevesy from commercial zirconium by 
removing the hafnium content. 
The spectra were photographed with a Hilger 
quartz spectrograph of largest size, and in our 
preliminary work we have confined ourselves to the 
spectral region between 2500-3500 A.U., 
could be exposed in a single setting of the spectro- 
graph. The spectra were produced in an ordinary 
carbon arc, the salts being placed on the cathode. 
The lines which are given in the table below as the 
most prominent hafnium lines in the region mentioned, 
are all lines which were not visible in an intense 
spectrum of the purified zirconium, while their 
intensity increased gradually in the preparations 
which by X-ray analysis were found to contain 
hafnium in increasing amounts. In the last specimens 
prepared by Coster and Hevesy, and estimated to 
contain about go per cent. hafnium, the lines ascribed 
to hafnium were among the most intense lines in 
the spectrum. In the table is given the wave-length 
X in international A.U. in air, measured against 
iron normals, and an estimation of the relative 
intensity I in the usual scale (strongest lines denoted 
by 6). 

which ; 



Xv I A I 
255905 | 3 2845°75 5 295420 | 5 3181-00 | 3 
2637-00 4 2851-00 44 2964°85* 5 3189°65 2k 
2638-7o*} 4 2866-35* 6 3016°65 5 3206°10 3 
2668-25 3 2887-15 4 3018°25 4h 3249°70 3k 
270560 5 2889-60 5 3050°75 4 3291-10 3 
271380 | 4 2898-30* | 6 305695 | 44 | 3309°55 | 2 
2718-50 4 2904:40* | 4 3072-90 5 3310°35 4 
2761°65 6 2904°75* 4 3080:80 4 3312-82 5 
2766-90 3 2916:50* | 6 3097°75 3 3332°70 5 
2773°05 4 2918+50 4 3156°65 4 3358"90 3 
2779°35 4 2924°55* 3 3159°80 4 3373°95 2 
281770 3 2929°90 4 3162-60 4h | 3472745 4 
2833°30 3 2940°80* | 6 3172°95 5 3497°40 4h 




We have examined the hafnium preparations for 
the presence of the lines belonging to the character- 
istic spectrum ascribed by Urbain (Comptes vendus, 
t. 152, IQII, p. 141) to an element celtium belonging 
to the family of rare earths, and the discovery of 
which was announced by him several years ago. 
By Dauvillier and Urbain (Comptes rendus, t. 174, 
1922, pp. 1347 and 1349; Nature, February 17, 
p. 218) this element was assumed to possess the 
atomic number 72. Not the slightest trace, however, 
of any of Urbain’s lines appeared on our plates. 
Although the minerals used as starting-point for 
the work of Coster and Hevesy contained rare earth 
elements in considerable amount, the only elements 
besides hafnium which could be detected spectro- 
NO. 2784, VOL. 111] 

as weak lines in zirconium spectra measured by 
earlier investigators. Thus Bachem (Diss., Bonn, 
1910) states the presence in his zirconium spectrum 
of the lines marked in the®*above table with an 
asterisk, and in several places he states without 
giving any measurements the presence of weak lines, 
which probably are identical with other of our 
hafnium lines. 
A fuller account of the hafnium spectrum, with 
measurements of the wave-lengths of the character-_ 
istic lines throughout the region which is obtainable 
photographically, will appear shortly. 
H. M. HANnsEN. 
S. WERNER. 
Universitetets Institut for teoretisk Fysik, 
Copenhagen, February 23. 

‘Echinoderm Larvez and their Bearing on 
Classification. 
THE object of my reply to Prof. MacBride (NATURE, 
December 16, 1922, p. 806) was not to discuss the 
classification of Asteroids, but to protest against the 
character of his unprovoked attack on me. An 
adequate discussion of the question which group of 
starfishes is the more primitive, the Phanerozonia or 
the Spinulosa, requires very much more space than 
that allotted to a correspondence in NATURE. What 
I wanted to prove—and, I think, did prove—was the 
want of foundation in Prof. MacBride’s sweeping 
statement that all admit the Spinulosa to be the 
more primitive group, tending to represent my view 
as to this point as perfectly absurd. 
Prof. MacBride now states (NATURE, January 13, 
p- 47) that in my original work I “ forgot that the 
Brachiolaria larva was found in Spinulosa but referred 
it to Forcipulata only.’ It is difficult to understand 
how I could have forgotten this, seeing that I have 
myself reared the larva of Asilervina pectinifera and 
found it to be a Brachiolaria ; moreover, in the v 
place (p. 220) where I arrive at the cbjectiongaae 
conclusion that the Brachiolaria is a specialised, not 
a primitive larval form, I begin with this statement : 
‘“ While it would thus appear to be a rule that the 
larve of the Phanerozonia have no Brachiolaria- 
stage, the facts known of the development of the 
Spinulosa and the Forcipulata (Cryptozonia) seem to 
indicate that their larve are characteristic through 
having a Brachiolaria-stage.” 
that, before thus criticising my work and accusin, 
me of omissions, of which I am not guilty, or fe 
absurd opinions (e.g. of regarding the metamorphosis 
of Echinoderms as metagenesis), which I have never 
set forth, Prof. MacBride would, at least, read the 
questionable paragraphs in that work ? I have never 
stated that the case of the regenerating larva, 
Ophiopluteus opulentus, even if it undergoes complete 
metamorphosis a second time, must alter our views 
as to the signification of Echincderm larve in general, 
only that this would represent a quite exceptional 
and unique case of metagenesis among Echinoderms. — 
Regarding the classification of Asteroids I will say 
only that the physiological and anatomical reasons 
given by Prof. MacBride for regarding the Astro-— 
pectinids ‘‘as Asteroids secondarily modified for a 
life on sand ’’ would scarcely be accepted as a sound 
basis for classification by any modern specialist on 
Asteroids, those ‘‘ students of the external features 
of preserved specimens only,” as Prof. MacBride 
rather contemptuously characterises them. May I 
only direct Prof. MacBride’s attention to the fact that 
Is it too much to ask © 
