March 24, 1870| 
the considerate courtesy with which they have been treated 
by gentlemen who differ very widely from my conclusions. 
1. Regarding the use of the spectroscope in the observation 
of ‘‘contacts.” 
I think the language of Mr. Stone and some others in a dis- 
cussion of the matter at a meeting of the Astronomical Society, 
reported in your columns in December last, implies a misappre- 
hension. What I have proposed (and executed in the case of 
the moon) is to use the extinction of the bright C line in the 
spectrum of the chromosphere as a criterion of contact with the 
limb of the phofosphere, not with the upper surface of the chromo- 
sphere, which would, of course, as indicated by Mr. Stone, be 
a perfectly worthless observation. 
The advantage of the method lies in this, that it furnishes an 
easily apprehended phenomenon to be watched for, and gives 
every advantage of preparation to the observer. 
With an instrument of moderate dispersive power, the slit 
must be normal to the sun’s limb, and an accurate knowledge of 
the expected point of contact is required : with a more powerful 
instrument the slit can be placed tangential, opened somewhat 
widely, and thus all difficulty on this score avoided, as I have 
pointed out in my report. I see by a paper of Mr. Proctor’s 
in the December number of the “ Monthly Notices,” that Mr. 
Huggins suggests the same plan. 
Perhaps I may remark in passing that the idea of using the 
spectroscope in this manner to observe the contact of the moon 
with the sun’s disc, was conceived before the event, so that the 
observation was made deliberately and by pre-arrangement—not 
at all accidentally, as would rather seem to be implied by one of 
the opening sentences in the article of Mr. Proctor’s above re- 
ferred to. To M. Faye, however, belongs whatever merit there 
may be in the method, for he proposed essentially the same thing 
in January 1869. But I knew nothing of this at the time of the 
eclipse, nor indeed till long after. 
2. The self-luminosity of the Corona. 
It is not impossible that the so-called corona may be complex. 
Some portion of its radiance may ferhaps originate in our own 
atmosphere, although I do not yet find myself able to accord 
with the conclusions of Dr. Gould and Mr. Lockyer in this 
respect, and am strongly disposed to believe that the whole 
phenomenon is purely solar. 
This much appears certain, however, that there exists outside 
of the chromosphere properly so called (?.¢., the envelope of red 
Aydrogen), and as distinct from 7, as it is from the photosphere, 
an immense atmosphere of self-luminous substance, extending to 
a distance of from 5/ to 8’ from the sun’s surface, and probably 
much further in places—phosphorescent dust or fog in a glowing 
as. 
: In support of this idea I adduce the photograph of Mr. 
Whipple, taken at Shelbyville, Ky., with an exposure of go> On 
this, the phofolytic corona (if I may use the expression to dis- 
tinguish it from the wisib/e corona, whose points of maximum 
brilliance were, according to Dr. Gould, entirely different), 
reaches a height of 6’. Prof. Harkness observed the 1474 
line in the spectrum of the corona at a distance of nearly 5° 
from the sun’s limb, and not near to any prominence. I do 
not know the precise elevation at which I saw it, but it was 
not less than 3’ or 4’. 
Indirectly, also, the idea is confirmed by the spectroscopic 
observation of Prof. Pickering, who used a single prism in- 
strument, with the slit simply directed towards the sun, not 
attached to a telescope. He saw only three or four lines, the 
brightest in the green near E. Now, since this line, when 
observed by throwing a large image of the sun on the slit, is 
very faint as compared with C, Dg, and F, its intensity, as seen 
by him, can only be accounted for by supposing that the 
luminous area from which it was derived far exceeded that of 
the chromosphere and prominences. 
I have noticed also that some of the observers of the Indian 
eclipse (Rayet and Pogson) speak of the intensity of the green 
line. Did they observe in the same manner as Prof. Pickering ? 
I need hardly add that Prof. Pickering’s observation of the 
non-polarisation of the corona concurs with what has been said. 
As to the faint continuous spectrum, I am sure that the 
reported absence of dark lines was not the result of insufficient 
observation. 
T could not have failed to see D, E, 4, 1961, Fand G had they 
existed, for in a spectrum of similar brightness formed by a light 
from a cloud, not only these but many other lines are visible in 
my instrument. Now, the absence of some of these might, 
perhaps, be accounted for on the ingenious hypothesis proposed 
NATURE 
533 
by Mr. Lockyer, and reported in your No. of February 3; but 
this would not apply to D, E, or G.* 
But if we admit the existence of faintly luminous solid or 
foggy matter near the sun, either meteoric or arising from the 
cloudy condensation of a non-permanent gas, the whole is at 
once easy of comprehension. 
3. The Auroral Theory of the Corona. 
The objection pressed by Mr. Lockyer that the bright line 
1474 is only occasionally visible, is, I think, unfounded. At any 
rate I have never failed to see it myself when looked for, and 
very seldom to make it visible to others when I have wished to 
exhibit to them. It is faint, and, like a difficult microscopic 
object, requires management to bring it out with five prisms ; 
but by placing the slit tangential to the sun’s disc, and giving the 
instrument a slight jar, it is seen to flash out as the limb passes 
off the slit. It is worth noting too, that it is often especially 
plain at portions of the limb where the chromosphere is unusually 
shallow and faint. 
But while I think it probable that this line coincides with the 
aurora line reported by Prof. Winlock at 1550 of Mr. Huggins’ 
scale, I am by no means sure of it. I understand its assigned 
position rested upon a single observation with a chemical spectro- 
scope, and the probable error of such a determination cannot 
well be less than ten divisions of Kirchhoff’s scale. I have 
naturally made many attempts to determine its position for my- 
self, but have never seen it except thrice, and then not long 
enough at a time to complete a measurement. Iam only sure that 
its position lies between 1460 and 1490 of Kirchhoff. 
For this reason, although I do not at all abandon the hypothe- 
sis, which appears to have other elements of probability in the 
general appearance of the corona, the necessity of intense elec- 
trical disturbances in the solar atmosphere as the result of the 
powerful vertical currents known to exist there, as well as the 
curious responsiveness of our terrestrial magnets to solar storms ; 
yet I do not feel in a position to urge it strongly, but rather await 
developments. 
As to the substance which causes this line, I observe that 
Father Secchi, ina recent communication to the French Aca- 
demy, is disposed to think it hydrogen ; while Mr. Lockyer still 
believes it to be iron. Iam in hopes that experiments now in 
progress may throw some light on the subject. 
May I suggest, in closing this long communication, that it 
seems to me that valuable observations might be made at the 
Eclipse of next December, by fitting up telescopes with a 
ground glass sliding screen, upon which an image of the corona 
two or three inches in diameter should be thrown ; the ground 
glass having the roughened side next the observer, so that he 
could sketch upon it with a lead pencil the outlines of the 
image, the glass being made long enough to allow of several such 
sketches. 
The comparison of a series of such outlines would decide the 
question of changes in the coronal streamers, as the sketches, 
being simple tracings, could not but be accurate in their in- 
dications of position. 
Dartmouth College, N.H., March 1 C. A. YOuNG 
P.S.—I think that the position of the line reported by me as 
2602 should have been 25$1°5, an error of one revolution of the 
micrometer screw having been made. At any rate on two oc- 
casions since the eclipse I have seen a bright line in the latter 
position, and I have never been able to find one in the former. 
Professor Huxley’s Address 
May I be permitted to advert to one view in connection with 
that part of Professor Huxley’s admirable address to the Geolo- 
gical Society, which treats of distributional provinces inhabited 
by the terrestrial vertebrata, and the subsequent incorporation of 
these provinces into one another at different periods. 
The view to which I refer is that wherein Mr. Huxley attri- 
putes the origin of the eocene types to their evolution during the 
Mesozic epoch in some province which then was isolated from 
the European area, and their introduction by geographical changes 
into the European area in the interval between the Mesozoic and 
Tertiary epochs. 
Having brought forward ten years ago the view that the Aus- 
tralian province was an actual and isolated remnant of the 
Triassic continent and of its mammalian fauna ; and that the 
geographical distribution of organised beings pointed to the infe- 
rence that other portions of the land tracts of the Mesozoic 
period, with their more ancient faunze, had at different times 
* Why not? [Ep.] 
