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252 ‘ 
SOLAR PHYSICS* 
In. 
you will recollect that in my last lecture I explained to you 
the ont absorptions that were due to certain hy 
carbons. To-day I wish to tell you some of the applications that 
can be made from an investigation and examination of this series. 
Before I proceed farther I wish to show you not only that there 
are absorptions which are due to the vibration of the atoms of 
these hy carbon molecules, but also that there is a general 
eoren which seems due to the molecular vibration of these 
same ape 
I wish to point out to you the general absorptions of the first 
three of those spectra, the alcohol series. The first one is methyl 
alochol which has a light molecule, or rather, 1 may say that 
it is lighter than the molecule of the next, common alcohol which 
in its turn again is lighter than propyl alcohol. You will see that 
the general absorption creeps up from the ultra-red towards 
the red. In each case the lighter the molecule the more 
vigorous is the general absorption. I was obliged to refer to this, 
because through the course of my lecture you will see that this 
has an important bearing on some of the results which we got. 
Another point is the effect of heat upon this general absorp- 
tion ; and here I speak with a certain amount of diffidence.. My 
belief is that the general absorption is increased by an increase 
of temperature in the hydro-carbons, in water, or in any of those 
liquids which we examined. Thus, with water, we find that 
the general absorption creeps up, the hotter the water is. In 
fact, at this time of the year when the temperature is high, it is 
very hard indeed to get some of those special absorptions very 
far down in the ultra-red, because: they are blocked out, as 
it were, by the general absorption which is due to the vibrating 
NATURE ans 
molecules—molecules of course vibrating in the manner which | 
I have described. 
The hydro-carbons which we have examined were all in the 
iguid state, and it seems very probable—nay, more than pro- 
je—almost certain,—that if you were to convert those liquid 
hydro-carbons into gas you would get their absorptions in the 
same localities. [For instance, in the diagram (Fig. 14) I will 
Fic. 1¢.—A bsorption spectra of liquid and gaseous bromine. 
show_you the absorption spectram of bromine. The top spectrum 
is the absorption ee. of baa bromine, and the bottom 
Spectrum is the spectrum of gaseous bromine. 
the difference between Pie is that, where you have the 
general absorption in the liquid, it is split up into lines in the 
case of the vapor. Thus in the case of the liquid we have 
the blue end of the spectrum entirely cut off by a general absorp- 
tion gradually increasing from the blue to the green. When we 
pass to the gaseous bromine we have the same absorption but 
terminated with bands. I do not say that this is always the case 
in bodies which have the same chemical constituents. 
Now, so far having cleared the ground for our next point, 
I must refer you back to-the map of the infra-red of the solar 
spectrum which I alluded to last ime. After we had completed 
‘You wil set that | hydro-carbon. I have here a small diagram showing what we 
our map of the ultra-red absorption spectra of these different | 
hydro-carbons, we had the curiosity to look at the map of the 
salar spectrum to see whether we could discover anything at all 
in relation between the two. Col. Festiig and myself were very 
surprised to find that we had mapped lines identical with lines in 
the ultra-red region of the solar spectrum. Thus, for instance, 
when we looked at the spectrum of water—we found that one 
line lay in the little @ group, and had a wave length of $33. 
When we cxamined chloroform, we also found that it had a 
| might expect to see. 
great many lines which we suspect are to be found in the solar | 
spectram. We then went to ethyl iodide, and here wealso found 
coincidences; but the coincidences were more marked than 
in the former case. For instance, last time I told you that, in 
order to identify the base or radical band of any particular hydro- 
* Lecture delivered on May 25, 2581, at the 
sington Museum, by Capt. Abney, R.E., F.R.S. Continued from p. rot. 
carbon, it was necessary to look for the base or radical, and, if 
need be, to confirm it by looking at other bands which were 
situated somewhere about the little a in thesolar spectrum, In 
the case of ethyl iodide we found that the band about little a 
coincided with part of the band in the solar spectrum. We also 
found that all of the alcohol series had one strong line coinci- 
dent with a solar line; other lines were also to be found 
coincident with other lines of the solar spectram. Furthermore 
the relative intensities of the lines in the liqnid and solar 
absorption spectra seemed identical. 
What, then, was the conclusion which we had to draw from 
this? Itwas that the lines in the solar spectrum must have 
something to do, or must have some connection at all events, 
with the lines found in the hydro-carbon series. 
Now, as I have said, where you havea liquid you need not 
expect the spectrum to be so minutely cere with lines as you 
would if you had the body in the gaseous state, and, in all pro- 
bability, suppose that we could have ethyl iodide in a gaseous 
state which is a thing not impossible to have—{it is very . 
only it is difficult to get enough of it)—those radical bands would 
probably split up into fine lines, and from the preliminary ex- 
periments which we have made it seems as if that would 
really be the case. But as this of course 1s 2 work of onlya 
few months old, this requires confirmation; and Col. Festing 
and myself propose to carry ont with vapour what we have 
already carried out with liquids. In our own minds there is no 
doubt that some at least of the hydro-carbons we have examined, 
are to be found in the solar spectrum, and we are also inclined 
to think that the hydro-carbons are not combined with oxygen, 
because, were they combined with oxygen, we should ex to 
find a more complicated spectrum of these particular lines or 
bands in the solar spectrum. 
Now suppose that we have such a compound as an ethyl com- 
pound of some description in the solar spectrum. Where can 
such a compound exist? It must exist in one of two places. It 
must exist near the sun, or it must exist in.our own atmo- 
sphere. Now the nearer you go to the sun of course the 
hotter the region, and it is quite impossible that these hydro- 
carbons, whatever they may be, should exist very near to the 
solar disc er to the nucleus. But if they do exist in the solar 
atmosphere at all they must exist at some little distance from 
them in a cooler region. You will recollect that Mr. Lockyer 
pointed out very clearly that there are regions around the solar 
nucleus which have vastly different temperatures. 
Now the question is, what compounds could exist even at 
a comparatively low temperature. There is a gaseous body 
allied to the ethyl series which would have the same radical or 
base bands, namely, acetylene. Acetylene can exist at a high 
temperature ; it has been found in the cooler part of the are of 
the electric light, but we also know that three of its molecules 
will combine to form benzine. Let us see what we should get, 
suppose that we have a ring of this hydro-carbon outside the sun; 
and then let us see what evidence would prove the presence of this 
12, 1882 . 
Fic, 15.—Solar disc surrounded with a hydrocarban ring. 
The black dise is supposed to be the solar 
nucleus, and this black ring which you see round it is supposed 
to be the ring of a hydro-carbon. The slit of the spectroscope 1s 
also shown. Now, if it exists at some little distance from the solar 
nucleus, you will see that when the light passes from the edge of 
the sun through that ring and then through the slit of the spectro- 
scope, it will pass through a deeper layer of matter than it would 
supposing the light came from the centre. In some photographs I 
| took of the solar spectrum some time ago, before we made these 
Lecture Theatre, South Ken- | apparentiy are 
t 
experiments, I found that some of the lines were more broadened 
at the limb of the sun than were other limes; and these lines 
coincident with these hydro-carbon lines. So, 
you see, from an examination of the hydro-carbons and an exam- 
