Dec. 22, 1881 | 
absorption will cover three hydrogen lines, and so on. Where 
you kaye lines, the lines never alter ; where you have those base 
bands, or radicle bands, as they are called, they never alter ; they are 
always in the same position, and never spread out or diminish 
either to the right or left. When you diminish the thickness of 
the fluid those bands are always present, and they are the last 
things to disappear in the absorption spectra. 
Another remarkable thing with regard to these compounds is, 
as arule there are two bands which are characteristic of their 
base. There is a band which is nearly always situated near the 
limit of the red, and another between wave-lengths 8000 to 
11,000, That is to say, there is always a band to be seen some- 
where about ‘‘a@,” and another somewhere about p. Those are 
characteristic of any particular compound we may have present. 
You may say that I have been giving you a lecture on chemis- 
try but in reality it is one which I hope may lead to results in 
solar physics. And I now venture to tell you how (Fig. 12). Here 
N°/Aldehyde 
N° Paraldehyde 
Fic. 12.—Absorption spectra of aldehyde and par-aldehyde. 
isa pair of bodies which we examined, to which I wish to 
draw your particular attention, namely, the spectra of alde- 
hyde and par-aldehyde. Now aldehyde and par aldehyde are 
the same bodies exactly in composition, only chemists tell us that 
yar-aldehyde has three molecules of aldehyde in its one mole- 
culc—the only difference then between them is that there are 
three molecules of aldehyde combined to form par-aldehyde ; 
aldehyde of course being one molecule by itself. Not only do 
chemists tell us that this is the case, but they know it, because 
if taey heat par-aldehyde they get aldehyde formed again, and 
can reconvert this into par-aldehyde. Now I want you to notice 
the difference in the spectra between these two bodies. We 
have two bodies of the same chemical composition and of dif- 
ferent molecular groupin, and you will see there is a total 
distinction in the two absorption spectra they yield. The only 
thing in common is the radical band. There may be one or 
two other coincidences, but all the rest of the spectra are 
perfectly distinct. Now if you refer back to Mr. Lockyer’s 
lectures I think this alone will throw some light on what he has 
already said to you. He has told you, for instance, that the 
spectrum of iron in the flames and the spectrum of iron in the 
Fic 
i three iron lines as observed by Lockyer. 
spots are dissimilar; and he has kindly furnished me with a 
photograph «hich shows one little part of the spectrum in which 
this is exem) lified in a remarkable degree. In it we have three 
iron lines close to one another (Fig. 13). In the sun-spots two 
NATURE 
191 
If you look at this by the light of that photograph of aldehyde 
and par-aldehyde which I had on the screen, I think it is a 
reasonabl: deduction to make that the iron in the flame and 
that in the sun-spots have different molecular groupings. I say 
that this spectral analysis to which we have subjected aldehyde 
and par-aldehyde, and many other similarly constituted bodies, 
lends confirmation to that view. Of course, in the case of organic 
compounds, we can appeal to the chemist to analyse them for us, 
and he tells us that they are different molecular groupings. It 
is scarcely fair in one case to admit that the two spectra are given 
by two molecular groupings of the same substance, and in the 
other to deny it. 
Again, we found that many lines were common to each hydro- 
carbon: thus we found a line at 867 of the scale, common to 
benzine and to alcohol; and to take one particular case, we 
found a special line common to water, hydrochloric acid, and 
chloroform, Has this any bearing on what you have heard ? 
Mr. Lockyer has told you that some short lines are to be found 
in two, three, four, or even six different metals, not taking the long 
lines into account, as they might be considered to be due to im- 
purities in the different spectra. Let us apply this to our case. A 
certain substance, A, has certain lines coincident with B; B also 
has certain lines coincident with C; and C also has other lines 
coincident with A. Now we will suppose these hydrocarbons 
were looked upon as elements, but that eventually the che- 
mists split up what they considered elements, and found that 
the only substance which was common to the three was hydro- 
gen. I leave you to draw the parallel between Mr, Lockyer’s 
experiments and those which I have endeavoured, ina very rough 
and unsatisfactory manner, to bring before you. I think, if 
the chemist will admit that in the case of the hydrocarbons it is 
hydrogen which produces the lines common to all, there is no 
reason on earth, supposing the metals are not elements, why you 
should conceive that they should not have a common con- 
stituent in the same way that the organic compounds have a 
common constituent in the shape of hydrogen, I leave that for 
your consideration, 
UNIVERSITY AND EDUCATIONAL 
INTELLIGENCE 
OxrorD.—Among the professorial notices of next term’s lec- 
tures already published are those of the Professors of Astronomy, 
Geology, Botany, and Medicine, 
Prof. Pritchard will give three courses at the University Ob- 
servatory. He will lecture on the Lunar and planetary Theories, 
and will form two classes for practical instruction in the evenings. 
Prof. Prestwich will lecture on Stratigraphical Geology in the 
University Museum, Prof. Lawson will lecture on the Elements 
of Systematic Botany at the Botanic Garden. 
The Professor of Medicine, Dr. Acland, gives notice that the 
next examination for a Radcliffe Travelling Fellowship will com- 
mence in the second week of February. Candidates are requested 
to communicate with the Professor, 
The professors and lecturers engaged in teaching Physics have 
settled a combined system of lectures for next term as below :— 
Hydromechanics, by Prof. Price; (1) Distribution of Ter- 
restrial Magnetism, (2) Electricity developed by Contact of 
different Substances, by Prof. Clifton ; Instruments and Methods 
employed in Optical Measurements, by Prof. Clifton ; Practical 
Physics, by Pro*. Clifton, Mr. Stocker, Mr. Heaton; The 
Generation and Measurement of Electric Currents, by Mr, 
Baynes; Electrostatics (treated Mathematically), by Mr. Hayes ; 
Elementary Mechanics (treated Experimentally), by Mr. Stocker ; 
Problems in Elementary Mechanics and Physics, by Mr, Heaton ; 
Elementary Physics treated Experimentally (Heat and Light), by 
Mr. Dixon. The lectures on Optical Instruments are intended 
to serve as an introduction to the practical work in the labora- 
tory. ‘The last three courses of lectures are intended to meet 
the requirements of candidates for the Preliminary Honour 
Examination. 
An examination for a Fellowship in biological subjects 
will be held at University College in February, 1882, be- 
ginning on Wednesday, February 22, at 9 a.m. Candidates 
are desired to call on Mr. C, J. Faulkner with the usual testi- 
monials and certificates on Tuesday, February 21, between 5 
and 6 p.m. But intending candidates are desired to send in their 
names to him before February 1, 1882, with a list of the subjects 
which they offer for examination, and at the same time to men- 
of those only a pear, and in the flames the third alone “appears, | tion any branch of biology to which they have turned special 
