196 
NA LORI 
[ Dec. 16, 1869 
Other Lines. 
Jron,... 1474. June 6, 1869. 
u 15155. June 6, 1869. 
Bright line 1529°5. July 5, 1869. 
? 1567'5. March 6, 1869. 
? 1613'8. June 6, 
Iron.... 1867°0. June 26. 
Bright line 187175. 90 
Tron ss... 20015) 
rm 2003 ‘4. 3 
? band or line near black 
line, very delicate . . pOOA e: 
July 5. 
Other lines besides these have been seen at different times ; 
but their positions haye not been determined absolutely. 
The author points out that taking iron as an instance, and 
° 
assuming that the iron-lines mapped by Angstrom and Kirchhoff 
are due to iron only, he has only been able, up to the present 
time, to detect three lines out of the total number (460) in the 
spectrum of the lower regions of the chromosphere, —a fact full 
of promise as regards the possible results of future laboratory 
work. The same remark applies to magnesium and barium. 
The paper then proceeded as follows :— 
“Dr. Frankland and myself have determined that the widening 
out of the sodium-line in the spectrum of a spot which I pointed 
out in 1866, and then stated to be possibly an evidence of greater 
absorption, indicates a greater absorption due to greater pressure. 
“The continuous widening out of the sodium-line ina spot must 
therefore be regarded as furnishing an additional argument (if 
one were now needed) in favour of the theory of the physical 
constitution of the sun first put forward by Dr. Frankland and 
myself—namely, that the chromosphere and the photosphere 
form the true atmosphere of the sun, and that under ordinary 
circumstances the absorption is continuous from the top of the 
chromosphere to the bottom of the photosphere, at whatever 
depth from the bottom of the spot that bottom may be assumed 
to be. 
“This theory was based upon all our observations made from- 
1866 up to the time at which it was communicated to the Royal 
Society and the Paris Academy of Sciences, and has been 
strengthened by all our subsequent work ; but several announce- 
ments made by Father Secchi to the Paris Academy of Sciences 
and other learned bodies are so opposed to it, and differ so much 
from my own observations, that it is necessary that I should 
refer to them, and give my reasons for still thinking that the 
theory above referred to is not in disaccord with facts. 
“ Father Secchi states that the chromosphere is often separated 
from the photosphere, and that between the chromosphere and 
the photosphere there exists a stratum giving a continuous spec- 
trum, which he considers to be the base of the solar atmosphere, 
and in which he thinks that the inversion of the spectrum takes 
lace. = 
“ With regard to the first assertion, I may first state that all the 
observations I have made have led me to a contrary conclusion. 
Secondly, in an instrument of comparatively small dispersive 
power, such as that employed by Father Secchi, in which the 
widening out of the F line at the base of the chromosphere is 
not clearly indicated, it is almost impossible to determine, by 
means of the spectroscope, whether the chromosphere rests on 
the sun or not, as the chromosphere is an envelope and we are 
not dealing merely with a section. But an instrument of great 
dispersive power can at once settle the question ; for since the 
F line widens out with pressure, and as the pressure increases as 
the sun is approached, the continuous curvature of the F line 
must indicate really the spectrum of a section ; and if the chro- 
mosphere were suspended merely at a certain height above the 
photosphere, we should not get a widening due to pressure : but 
we always do get such a widening. 
“With regard to the second assertion, I would remark that if 
such a continuous-spectrum-giving envelope existed, I entirely 
fail to see how it could be regarded as a region of selective ab- 
sorption. Secondly, my observations have indicated no such 
stratum, although injections of sodium, magnesium, &c. into the 
chromosphere not exceeding the limit of the sun’s limb by 2” 
have been regularly observed for several months past. To-day 
T have even detected a low level of barium in the chromosphere 
not 1” high. ‘This indicates, I think, that my instrument is not 
lacking in delicacy ; and as I have never seen anything approach- 
ing to a continuous spectrum when my instrument has been in 
perfect adjustment, I am inclined to attribute the observation to 
some instrumental error. Such a phenomenon might arise from 
a local injection of solid or liquid particles into the chromo- 
sphere, if such injection were possible. But I have never seen 
such an injection. If such an occurrence could be observed, it 
would at once settle that part of Dr. Frankland’s and my own 
theory, which regards the chromosphere as the last layer of the 
solar atmosphere; and if it were possible to accept Father 
Secchi’s observation, the point would be settled in our favour. 
“The sodium experiments to which I have referred, however, 
and the widening out of the lines in the spot-spectra, clearly 
indicate, I think, that the base of the atmosphere is below the 
spot and not above it. I therefore cannot accept Father Secchi’s 
statement as being final against another part of the theory to 
which I have referred—a conclusion which Father Secchi him- 
self seems to accept in other communications. 
‘‘Wather Secchi remarks also that the F line is produced by the 
absorption of other bodies besides hydrogen, because it never 
disappears. This conclusion is also negatived by my observa- 
tions ; for it has very often been observed to disappear altogether 
and to be replaced by a bright line. At times, as I pointed out 
to the Royal Society some months ago, when a yiolent storm is 
going on accompanied by rapid elevations and depressions of the 
prominences, there is a black line on the less-refrangible side of 
the bright one; but this isa phenomenon due to a change of 
wave-length caused by a rapid motion of the hydrogen. 
“With regard to the observation of spot-spectra, I find that 
every increase of dispersive power renders the phenomenon 
much more clear, and at the same time more simple. The 
selective absorption I discovered in 1866 comes out in its most 
intense form, but without any of the more complicated accom- 
paniments described by Father Secchi. I find, however, that 
by using three prisms this complexity vanishes to a great extent. 
We get portions of the spectrum here and there abnormally 
bright, which have given rise doubtless to some of the state- 
ments of the distinguished Roman observer; but the bright 
lines, properly so-called, are as variable as they are in any other 
part of the disk, but not much more so. I quite agree that the 
‘interpretation’ of sun-spot phenomena to which Father 
Secchi has referred, * which ascribes the appearances to anything 
but selective plus general absorption, is erroneous. But as I 
was not aware that it had ever been propounded, I can only refer 
to my own prior papers in support of my assertion which were 
communicated to the Royal Society some three years ago.” 
“Researches on Gaseous Spectra in relation to the Physical 
Constitution of the Sun, Stars, and Nebulz.”—Third Note. By 
E. Frankland, F.R.S., and J. Norman Lockyer, F.R.S. 
The authors remark that it has been pointed out by Mr. 
Lockyer that the vapours of magnesium, iron, &c., are some- 
times injected into the sun’s chromosphere, and are then rendered 
sensible by their bright spectral lines. (Proc. Roy. Soc., vol. xvii. 
p. 351.) 
2. It has also been shown (1) that these vapours, for the most 
part, attain only a very low elevation in the chromosphere, and 
(2) that on rare occasions the magnesium vapour is observed like 
a cloud separated from the photosphere. 
3. It was further established on the 14th of March, 1869, and 
a drawing was sent to the Royal Society indicating, that when 
the magnesium vapour is thus injected, the spectral lines do not 
all attain the same height. 
Thus, of the d lines, 61 and 4° are of nearly equal height, but 
64 is much shorter. 
4. It has since been discovered that of the 450 iron lines ob- 
° 
served by Angstrém, only a very few are indicated in the spec- 
trum of the chromosphere when iron vapour is injected into it. 
5. The authors’ experiments on hydrogen and nitrogen enabled 
them at once to connect these phenomena, always assuming that 
the great bulk of the absorption to which the Fraunhofer lines 
are due takes place in the photosphere itself. 
It was only necessary, in fact, to assume that, as in the case 
of hydrogen and nitrogen, the spectrum became simpler where 
the density and temperature were less, to account at once for the 
reduction in the number of lines visible in those regions where, 
on the authors’ theory, the pressure and temperature of the ab- 
sorbing vapours of the sun are at their minimum. 
6. It became important, therefore, to test the truth of this 
assumption by some laboratory experiments, the preliminary re- 
sults of which are communicated in this note. 
* Comptes Rendus, 1869, 1 sem, p. 764. 
