106 
precisely to the category of those which reverse them- 
selves ; for some are reversed and the others are on the 
point of being so. For the same metals, the reversals are 
more or less complete according to the conditions of the 
experiment, and for different metals according to their 
chemical and physical properties. 
The law of distribution of these groups presents another 
common character relatively to the succession of distances 
and intensities : the lines get nearer together towards the 
more refrangible end, and diminish in intensity. This cha- | 
racter is much the more striking when the number of 
reversed lines is considerable, because the field on 
which they appear is more uniform. It seems that with 
the elevation of temperature the spectrum tends towards 
a limit, that of a continuous brilliant background despoiled 
of all lines except the regular series of the self reversing 
ones. It is to this constitution that I wish to draw the 
attention of observers. 
The number of metallicspectra capable of giving a regular 
Ser ies of spontaneously reversed lines ona contintious back- 
ground is considerable ; but the most beautiful series that 
I have observed were supplied by two metals which one 
could scarcely have anticipated, from a chemical point of 
view, to find side by side ; these are aluminium and thal- 
lium, whose equivalents are at the extremity of the list 
of those of the simple bodies. The diagram gives an 
idea of the distribution of these reversed lines ; one sees 
DESCRIPTION OF 
ultra-violet spectra of 
arc). 
doublet). 
© the white stars 
NATURE 
THE D1 AGRAM. — The graduations define the lines according 
The second represents a double series 
1e scale of the drawing has been chosen in a manner to make G and 6 coincide with the homologous lines of the first series (first line of each 
One could have operated in the same way with the second series (second lines). 
[ Fune 3, 1886 
that they form in each spectrum a series of doublets ful- 
filling the conditions of distance and intensity given 
above. 
I shall not stop to indicate the fruitless trials of numeri- 
cal calculations that I have taken in hand in order to 
represent each of these series by the substitution of the 
series of entire numbers in a simple function ; I may add 
that I had given up these researches until the discovery 
of Dr. Huggins on the spectra of white stars brought back 
my attention to this subject. 
These spectra present, in fact, a common series of dark 
lines, that is to say, reversed, fulfilling precisely the 
conditions of distance and intensity which characterise in 
metallic spectra the spontaneously reversed lines: they 
prolong the series of well-known lines of the spectrum of 
hydrogen, C, F, G, 2. One could then foresee that the 
whole series belonged to them; that is what has since 
been confirmed by Vogel, though this result is still not 
quite certain. The interest of this identification was such 
that I sought to prove it myself, which I could not realise 
till lately. ‘The experiment is not without difficulty ; but 
in taking more minute precautions to get rid of all im- 
purity in the hydrogen, I have seen the impurity lines 
obliterated, and finally I succeeded in obtaining photo- 
graphs showing the series of star-lines in all their purity. 
The spectrum of hydrogen is placed on the first line in 
the above diagram: the comparison has been rendered 
ALUMINIUM 
to their wave-lengths. The first line represents the dark lines of the violet and 
of inverted lines in the ultra-violet spectrum of aluminium (electric 
This mode of representation advantageously replaces the 
numerical tables, showing the verification of the two empiric formulas— 
First series aoe cr ap 
Second series 
which give the length of the wave of each line in function of the wave- 
calculation and the observation is of the order of the experiment: al errors. 
violet spectrum of thallium (electric arc). The scale of the drawing w 
series are :— 
A; = ¢ 
Ne 
easier by the choice of scales showing intuitively the 
identity of the law of distribution of lines in the three 
spectra, 
We might compare in the same way the more complex 
groups, like magnesium, zinc, sodium, &c. ; the only diffi- 
culty is to establish the agreement of the groups ; we do 
this immediately by a quite simple graphic construction. 
We arrive at the following statement, which resumes the 
whole of my researches. In the metallic spectra certain 
series of lines, spontaneously reversed, present sensibly 
the same law of distribution and intensity as that of the 
hydrogen lines. 
It is not necessary to dwell on the importance of this 
relation: it makes evident the existence of a law which 
is general relatively to the emissive powers of incandes- 
cent vapours, and, again, it shows that this law of suc- 
cession of spectral lines, common to so many series, seems 
to be expressed by the help of the same function, which 
one might call the hydrogenic function, which should | 
Ay = 47°30 + 0'43783 
” Az = 47°18 + 0°43678 1 
ster ngth % of the corresponding line of hydrog xen; the difference between the 
The third line represents a double series of inverted lines in the ultra- 
as chosen like the one above ; the empiric formulas which represent these two 
3 
play the principal part in these studies: the result then 
appears to constitute a first step towards the solution of 
the great problems which the spectroscope brings on for 
solution, R. 
VEGETATION OF SOUTH GEORGIA 
Capt. Cook landed on 
N Tuesday, January 17, 1775, 
this remote island, which is situated about 1000 
miles east of Cape Horn, in about 54° S. Jat. and 37° W. 
long.,and took possession of it in the name of King George 
the Third, after whom he named it. Capt. Cook landed in 
three different places, and the ceremony of adding theisland 
to the British dominions, he informs us, was performed 
under a waving of colours and a discharge of small arms. 
Whether any British subject has ever set foot on it since 
that day I know not; but the description of the island 
by its famous discoverer was not likely to tempt any one 
to go out of his way with that object in view. Although 
