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May 29, 1873] 
NATURE 
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around that sun (Aldebaran) in exactly the same way as 
_ round our own. We also get some of the iron lines, the 
lines of sodium, and the lines of hydrogen, calcium, and 
a few other elements—nine in all. At the basejof the 
diagram you see indications of the elements, with the 
bright lines of which Mr. Huggins has compared the 
black lines which you see in the spectrum of these 
heavenly bodies. By means of the star spectroscope and 
of the induction coil, Mr. Huggins tested these lines, as 
Kirchhoff did in the case of the sun, by actually getting 
the vapour of magnesium visible at the same time in the 
spectroscope: and thus you see in a moment that there 
is no difficulty at all in determining their coincidence, 
you have the two things brought so closely side 
by side. If I had time I might remark on the 
presence of some elements here and the absence of 
others ; but there is one remarkable fact about this lower 
star (a Orionis) which I must mention. As far as its 
spectrum goes, it appears that the gas hydrogen, which 
is a very important element in our sun’s atmosphere, as 
we gather from the great distinctness of the hydrogen 
lines in the solar spectrum—and not only in our sun, but 
in a great many others—is absolutely absent, whilst mag- 
nesium, sodium, calcium, &c., are present. 
So far, then, you see that this little prism has enabled 
us to read a great many secrets of the sun and of the 
more distant stars; and we must acknowledge that 
Stokes’ and Kirchhoff’s hypothesis is a very magnificent 
one, and we can but wish that there were more men like 
them, who, undismayed by the failure of those who, for 
nearly a century before their time. had been endeavouring 
to unravel these secrets, were still prepared to go on, and 
endeavour to find them out by means of a prism and a 
simple sodium flame. 
Now, astronomers—who, as I told you, from the time 
of Wilson had imagined that the sunspots were cavities— 
very soon began to quarrel with this hypothesis of Kirch- 
hoff’s, who said that the sunspots, instead of being 
cavities, were really clouds floating in the atmosphere. 
They remarked, and I think with truth, that to make 
such an assertion was altogether opposed to the evidence 
of the telescope. And I think I may say that the as- 
tronomers have now carried the day, for another line of 
independent research altogether—I mean the researches 
into the constitution of the sun by means of the spectro- 
scope—has come to the aid of the astronomers, and it 
looks very much as if we must still hold to the opinion 
that Wilson in his observations, now more than a century 
old, was perfectly right, and that Kirchhof’s analysis, as 
far as it deals with the sun-spots, is susceptible of im- 
provement. In the remarks I made in my former lecture 
on radiation in connection with the red prominences 
visible during eclipses, I drew your attention particularly 
to the hydrogen lines, and told you that the red flames 
are, for the most part, composed of hydrogen. There the 
prism comes to our aid in a very remarkable way indeed. 
It is clear to you, I think, after what I have said about 
absorption, that the darkening of the sun’s surface, which 
we call a spot, is really a thing about which the prism can 
tell us a great deal. For instance, take a sun-spot, in 
which the usual brilliancy of the sun inthe other parts of 
its disc is altogether wanting. There is not only great 
darkness here and there, but wonderful turnings and 
twistings and bendings of this solar envelope, which I 
have already told you Kirchhoff asserts to be a liquid 
one, but which I think a little consideration of Fig. 50 
will show you is more probably gaseous, or cloudy, than 
liquid. It is obvious, I say, in this case that there was a 
great probability of the spectroscope being able to tell us 
something about this absence of light, for an absence of 
light means one of two things ; it means either that there 
was a defect in radiation, or that there was some excess 
of absorption, and I miay say that this difference—which 
I hope you now all thoroughly understand—really formed 
the battle-ground between the English and French as- 
tronomers until a few years ago. Long after Kirchhoft’s 
experiment, M. Faye, a distinguished member of the In- 
stitute of France, went all over the work again, and de- 
clared that the sun-spot was dark, because we there got 
the light, not from the brightly shining envelope, but from 
some feebly radiating gas inside the sun; that the sun 
was a gigantic bubble, the bubble being nothing else than 
the photosphere—the liquid sphere of Kirchhoff—the 
interior being composed of gas, glowing at such an 
enormous temperature that the light we got from it was 
extremely feeble. You will see in a moment that, if the 
sun-spot were really due to the radiation from gas, we 
should get from that sun-spot a selective spectrum, that is 
to say,a spectrum with bright lines. The English as- 
tronomers said: “No; a sun-spot is not due to de- 
fective radiation at all ; there is something over the bright 
portion of the sun which eats away the light :” whether 
the light'was eaten away generally—whether, in fact, we 
had an instance of general or selective absorption—was 
not stated, but what they did distinctly state was, that the 
sun-spot was simply an indication of absorption. So 
that, you see, here was a thing which a spectroscope 
might settle almost at once, provided always that a good 
sunspot could be obtained for the experiment. This was 
done in 1866. Fig. 51 gives an idea of what is seen when 
we observe a small sunspot, and it is one which is full of 
meaning. Here is a very clear image of the solar spec- 
trum near the double line D, and also the double D itself, 
If it were possible to have given you the whole of the 
sun’s spectrum on the same scale as this, it would require 
an engraving yards in length, but it would be almost 
impossible to make my meaning clearer than I hope I 
can do by this small portion ; and~I must therefore ask 
you to take for granted that the dark line which you see 
running along this yellow portion of the spectrum would 
really run along the whole length of the spectrum, from 
the extreme red to the extreme violet. This, then, you 
see in a moment, was an indication of general absorption; 
that is to say, in the way in which the light is affected by 
its passage through the prism, we have the problem 
settled in an instant, that a sunspot is due to general 
absorption at all events. Further, in observing the 
spectra of different sunspots, it was found that the spec- 
trum of the middle of the sunspot is much darker than 
the outside. So that you see this simple experiment tells 
us not only that the sunspot is due to general absorption, 
but that there is more general absorption in the middle of 
the spot than at its edge. This is the way in which this 
little prism is able to deal with these great problems. 
J. NORMAN LOCKYER 
(Zo be continued.) 
MIND IN THE LOWER ANIMALS 
RECENTLY received a letter from Mons. J. C. 
Houzeau, the author of the “ ctudes sur les Facultés 
Mentales des Animaux comparées a celles de Homme,” 
published at Mons, Belgium, in 1872, and reviewed by 
Mr. Wallace in NATURE of October 10, 1872. The latter 
eminent writer asserts that M. Houzeau’s work “ contains 
a mass of curious facts, acute observations, and sound 
reasoning, which fully entitle its author to take high 
rank among philosophical naturalists” (p. 471). I quite 
agree with him in his estimate of M. Houzeau’s labours, 
being disposed to place his two volumes of “Etudes” on 
a par with the works of Mr. Darwin; and with another 
work, which, while little, if at all, known in this country, 
deserves, nevertheless, the highest consideration at the 
hands of all interested in comparative psychology—the 
“Traité de la Folie des Animaux de ses Rapports avec 
celle de ’!Homme,” by Dr, Pierquin, published in Paris 
(in 2 vols.), so long ago as 1839, - 
