Fan. 19, 1882] 
“NATURE 
263 
and so it may easily be the case that at solar temperatures 
certain of our terrestrial elements cannot exist, or, if they 
exist at all, can do so only in certain very restricted 
regions of the solar atmosphere. 
“One strong argument in favour of this view is found 
in the fact, now we think beyond dispute, that the same 
substance may, under different circumstances, give widely 
different spectra. ...” 
“There seem to be at least three possible explanations 
of these facts. One is, to suppose that the luminous 
* substance, without any change in its own constitution, 
vibrates differently and emits different rays under varying 
circumstances, just as a metal plate emits various notes 
according to the manner in which it is held and struck. 
The second assumes that the substance, without losing 
its chemical identity, undergoes changes of molecular 
structure (assumes allotropic forms) under the varying 
circumstances which produce the change in its spectrum. 
According to either of these views, although we can safely 
infer from the presence of the known lines of an element 
in the solar spectrum, its presence in the solar atmosphere, 
we cannot legitimately draw any negative conclusion ; 
the substance may be present, but in such a state under 
the solar conditions as to give a spectrum different from 
any with which we are acquainted. 
“The other and simplest explanation is to suppose, with 
Mr. Lockyer, that the changes in the spectrum of a body 
are indications of its decomposition, the spectrum of the 
original substance being replaced by the superposed 
spectra of its constituents.” 
“Another point which favours Mr. Lockyer’s view is 
this : Certain substances have numerous lines apparently 
common. Thus, if one runs over Angstrém’s map of the 
solar spectrum, he will find about twenty-five lines marked 
as belonging both to iron and calcium. The same thing 
is true of iron and titanium to a still greater extent, and 
to a considerable degree of several other pairs of sub- 
stances. This fact might be explained in several ways. 
The common lines may be due, first, to impurities in the 
materials worked with; or, second, to some common 
constituent in the substances (which is Mr. Lockyer’s 
view); or, third, to some similarity of molecular mass or 
structure which determines an identical vibration-period 
for the two substances ; or, finally, it may be that the 
supposed coincidence of the lines is only apparent and 
approximate—not real and exact—in which case a spec- 
troscope of sufficient dispersive power would show the 
want of coincidence.” 
“Now, Mr. Lockyer, by a series of most laborious re- 
searches, has proved that many of the coincidences 
shown on the map are merely due to impurities... .. 
But when all is done, we find that certain of the common 
lines persist, becoming more and more conspicuous with 
every added precaution taken to insure purity of materials. 
‘Moreover, when one of the substances, say the cal- 
cium, is subjected to continually increasing temperatures, 
its spectrum is continually modified, and these basic lines, 
as Mr. Lockyer calls them, are the ones which become 
increasingly conspicuous, while others disappear. This 
is just what ought to happen if they are due to some 
element common to both iron and calcium—an element 
liberated in increasing abundance with every rise of 
temperature ” (pp. 89-92). 
“©A given element often has several entirely different 
spectra. Changes, such as have been mentioned, go on 
up to a certain point, and then, suddenly, an entirely new 
spectrum appears, not having apparently the slightest 
connection with the one which preceded it any more than 
if it came from an entirely different element or mixture 
_ of elements ; as, in fact, according to Mr. Lockyer’s view, 
is probably the case. 
‘Now, in the solar spectrum, the dark lines charac- 
teristic of an element are all coincident with the bright 
lines of its gaseous spectrum ; but it is not often the case 
that the relative width and intensity of the solar lines 
match those of the bright lines in the spectrum obtained 
by artificial means” (pp. 96-97). 
“Tn the motion-distortions of lines Lockyer finds 
strong confirmation of his ideas. It not unfrequently 
happens that in the neighbourhood of a spot certain of 
the lines which we recognise as belonging to the spec- 
trum of iron give evidence of violent motion, while close 
to them other lines, equally characteristic of the labora- 
tory spectrum of iron, show no disturbance at all. If we 
admit that what we call the spectrum of iron is really 
formed in our experiments by the superposition of two or 
more spectra belonging to its constituents, and that on 
the sun these constituents are for the most part restricted 
to different regions of widely varying pressure, tempera- 
ture, and elevation, it becomes easy to see how one set of 
the lines may be affected without the other ” (p. 100-101). 
It will be gathered then from these extracts that in 
Prof. Young’s opinion, whatever that opinion may be 
worth, and we for our part attach great value to it, the 
new hypothesis does get rid of a good many of the 
difficulties of the old one, and surely this is the best 
justification any worker in science can have for sug- 
gesting an hypothesis. It is to be noted also that 
several of the various converging lines of evidence, espe- 
cially those depending on the changes in spectra, are 
referred to. It is imagined by some that the new hypo- 
thesis breaks down if a line apparently coincident in the 
spectra of two substances at small dispersion should turn 
out to be non-coincident when a higher power is em- 
ployed, while the fact is that the assumption that there 
should be such coincident lines, if we can reach a 
particular temperature, is based upon one manner of 
behaviour of compound bodies to the exclusion of 
another, and on such points as these we are as yet in 
profound darkness. 
The chapter on the sun’s light and heat, and the 
appendix on Prof. Langley’s recent work will well repay 
perusal. 
THUDICUM’S ANNALS OF CHEMICAL 
MEDICINE 
Annals of Chemical Medicine. Vols. 1.and Il. By J. 
L. W. Thudicum, M.D. (London: Longmans, Green 
and Co., 1879.) 
HOSE who open this work expecting to find it 
adequately fulfilling the promise of its title will be 
disappointed. Had they read the initial preface they 
would have been prepared for this, for it indicates very 
clearly the intention of the promised series, of which the 
first two volumes are now published. 
Dr. Thudicum is well known as the author of numerous 
researches in Animal Chemistry, which are chiefly re- 
markable for the large number of new bodies described 
in them, and the somewhat fantastic names he has 
assigned to these bodies. Somehow or other the results 
of these researches have not met with that general 
acceptance which their author desires ; indeed they have 
in many cases been either to a great extent passed over 
or else their value called into question by those who 
have repeated his experiments or worked at the same 
parts of the subject. This is clearly recognised by the 
author in the preface to the first volume, and has accord- 
ingly led him, on the assumption that one cause, among 
