154 
NATURE 
[Fune 19, 1873 
, ; 
The observations in this paper are a continuation of those 
referred to in the previous communication bearing the same title. 
They deal (1) with the spectrum of chemical compounds, and 
(2) with the spectra of mechanical mixtures. 
I. Chemical Compounds. 
Several series of Salts were observed; these series may be 
divided into two :—1st, those in which the atomic weights varied 
in each series; 2nd, those in which the associated elements 
varied in each series. The following salts were mapped :— 
Pb F,, Pb Cl, Pb Bra, Pb I,; Sr F,, Sr Cl, Sr Bra, 
SrI,; BaF,, Ba Cl, Ba Br,, Bal,; MgF,, Mg Cl., Mg Br, 
MgI,; NaF, Na Cl, Na br, Nal. 
The conditions of the experiments are described, the same alu- 
minium cups, described in the first paper, were used, and the 
poles were arranged in such a manner that they could at will be 
surrounded with any gas or vapour. Hydrogen was used in 
some of these experiments ; it was purified in the usual manner 
by drying, and freeing from traces of sulphuretted hydrogen, it 
was then passed over clean cut pieces of sodium, and admitted 
to the poles. An induction-spark from 5 one-pint Grové tells 
was used, the circuit being without the Leyden gar. 
The lead compounds behaved (in air) as follows :— 
The fluoride gave the eleven longest lines of the metal, but 
four were very faint. 
The chloride gave nine lines ; one of these is very short. 
The bromide gave six lines, but one is a mere dot on the pole. 
The iodide gave four lines distinctly and two as dots, one of 
which is scarcely visible. 
It is pointed out that the decrease in length and number of 
lines follows the increase in the atomic weight of the non-me- 
tallic element, the lines dying out in the order of their length. 
Barium was next experimented on, the same series of salts 
being used. A marked departure from the results obtained in 
the case of the lead compounds was observed especially in 
the case of the fluoride, its spectrum being much the simplest ; 
in fact it consisted of only four lines. Strontium behaved like 
barium, and so did magnesium fluoride. This anomalous be- 
haviour was found to be most probably due to the exceedingly 
refractory nature of these fluorides, all of them being quite in- 
fusible, and non-volatile in any spark that was used. 
Sodic fluoride, sodic chloride, sodic bromide, and sodic iodide 
exhibited a behaviour exactly the reverse of that of lead, z.¢. the 
iodide showed most of the metallic spectrum. 
The difference between flame-spectra and those produced by 
a weak electric discharge are then discussed. Beads of the 
chlorides, &c., were heated in a Bunsen-gas flame; Bal, gave a 
‘*structure” spectrum (since proved to be due to the oxide) and the 
line 5534°5, by very {ar the longest metallic line of barium; the 
beadiused. The bromide behaved like the iodide, and so did the 
chloride, except that its spectrum was more brilliant. Baric fluoride 
gave scarcely atrace of aspectrum, the oxidestructure being scarcely 
visible, and 5534°5 very faintindeed. The strontium salts follow 
those of barium, 4607°5, the longest strontium line appearing in 
conjunction with an oxide spectrum. The strontic fluoride, 
however, refused to give any spectrum whatever. These results 
are compared with those obtained with the weak spark, and it 
is shown that the difference is one of degree ; e.g. baric bromide 
gives 25 lines in the spark ; these are the longest lines. In the 
flame it gives but one line; but this is the longest of all the 
barium lines, and indeed very far exceeds all the others in 
length. When the flame-spectra are compared with those pro- 
duced by the low tension spark, the spectra of the metals in the 
combination are in the former case invariably more simple than 
in the latter, so that only the very longest line or lines are left. 
Some experiments made by Mr. K. J. Friswell to determine 
the cause oi the similarity of the spectra of the various salts of 
the same metal observed in air are then given, the conclusion 
being that the spectrum observed is really that of the oxide. 
\archhoff and Bunsen’s, Mitscherlich’s, and Clifton and 
Roscoe’s prior conclusions on the points investigated are stated 
at length ; and it is shown that the observations recorded, taken 
in conjunciion with the determination of the long and short lines 
of metailic vapours, are in favour of the views advanced by 
Muscherlich, Chitou, aud Roscoe. For while the spectra of 
the iodides, bromides, &c. of any element in air are the same as 
stated by Kirchhoff and Bunsen, the fact that this is mo¢ the 
spec.ra of the metal is established by the other fact, that only 
the very longest lines of the metal are present, increased dissociation 
bringing in the other metallic lines in order of their length, 
The spectra have been mapped with the salt in hydrogen ; 
here the spectra are different, as stated by Mitscherlich, and ¢he 
metallic lines are represented according to the volatility of the com- 
pound, onry the very longest lines being visible in the case of the 
least volatile one. 
The following are the conclusions arrived at :— 
1. A compound body has as definite a spectrum as a simple 
one ; but while the spectrum of theslatter consists of lines, the 
number and thickness of some of which increase with molecular 
approach, the spectrum of a compound consists in the main of 
channelled spaces and bands which increase in like manner. In 
short, the molecules of a simple body and of a compound one 
are affected in the same manner by their approach or recess, in 
so far as their spectra are concerned ; i other words, both spectra 
have their long and short lines, the lines in the spectrum of the 
element being represented by bands or channelled lines in the 
spectrumo “the compound ; and in each case the greatest sim- 
plicity oft Le spectrum depends upon the greatest separation of 
molecules, and the greatest complexity (a continuous spectrum) 
upon their nearest approach, 
2. The keat required to act upon a compound, so as to render 
its spectrum visible, dissociates the compound according to its 
volatility ; t he number of true metallic lines which thus appear 
is a measure of the dissociation, and doubtless as the metal lines 
increase in rumber the compound bands thin out. i 
Mitscher ich’s obvervations, that the metalloids show the same 
structurals pectra as the compound bodies is then referred to, 
and the question is asked whether the molecules of a metalloid 
do not in stiucture lie between those of elements on the one 
hand and compounds on the other. 
These ccrsiderations are applied to solar and stellar spectra ; 
the general zppearance of the solar spectrum shows that in all 
probability there are no compounds in the sun. 
Secchi’s raps of a large number of stellar spectra are referred 
to as now incicating beyond all doubt the existence of compound 
vapours int he atmosphere of some stars; and it is suggested 
that the pheromena of variable stars may be due to a delicate 
state of equilibrium in the temperature of a star which now pro- 
duces the giezt absorption of the compound and now that of the 
elemental mclecules. 
The secord part of the paper deals with the mechanical mix- 
tures. Maps ¢f the spectra of alloys of the following percentages 
are given :— 
Sn and Cd _ percentages of Cd 
Pb and Zn 36 ee Zn 10'0, 50, 1°, OF. 
Phyatid Migeiets ila ubetes «ask Mg 10'0, 1°0, O'l, O’OI. 
It is pointed out that the lines die out in the order of their 
length as the percentage becomes less, the shortest lines disap- 
pearing first; and that although we have here the germs of a 
quantitative spectrum analysis, the method is a rough one only, 
but that furtker researches on a method which promises much 
greater accurecy are in progress, 
The bearing of these results on our knowledge of the reversing 
layer of the sun’s atmospheres is then discussed. 
Mathematical Society, June 12.—Dr. Hirst, F.R.S., 
president, in the chair.—The following papers were read :— 
‘‘Some general theorems relating to Vibrations,” Hon. J. W. 
Strutt; ‘‘Invariant conditions of multiple concurrence of three 
conics,” Mr. j. J. Walker; ‘‘On a new form of Biquaternion, 
being the ratic of two systems of forces,” Prof. Clifford; “* A further 
note on geodesic lines,’”’ Prof. Cayley —A paper by Prof. Wol- 
stenhoime, ‘* The locus of the point of concourse of tangents to an 
epicycloid, inclined to each other at a constant angle,” was, in 
the author’s absence, taken as read.— A conversation ensued on 
the subject of Prof. Clifford’s paper, in which the president, Prof, 
Cayley, and Mr. S. Roberts took part. 
Geological Society, May 28,—Prof. Ramsay, F.R.S., 
vice-president, in the chair. The following communications 
were read:—‘‘The Glaciation of the northern part of the 
Lake-district,” by J. Clifton Ward. The author stated the 
leading questions to be settled by his investigation of the 
northern part of the Lake-district as follows :—The fact of the 
glaciation of the district being granted, and of this he adduced 
abundant evidence, th= questious that arose were whether tue 
glaciating agent worked irom north to south, whether it came 
from within or from without the district, and finally, whether the 
agent was floating ice, a system of local glaciers, or an unbroken 
ice-cap. As the result of his investigation he maintained that 
there is no evidence that a great ice-cap from the north ever 
swept over this district. The ice-scratches trending along the 
100, 5‘O, IO, O'I5. 
