136 PROFESSOR PIAZZI SMYTH ON COMETARY PHYSICS. 
most forked about the perihelion, both on account of the greater absorption and reflection of light 
in passing through the denser anterior half, and on account of the greater ratio which the difference 
of distance of the anterior and posterior ends bear to that of the former and the sun; and at a 
distance from the perihelion, the effects being reversed, we might expect to see less phase, a less. dark 
axis in the tail, and something of a convergence in the limbs of it. Now, both of these phenomena 
were distinctly and markedly observable in the great comet of 1843; near the perihelion the tail 
being forked, the axis almost as dark as the sky round about, and the limbs intensely bright and 
sharp; but long before it was lost on its retreat to aphelion, the oval darkness was almost obliterated, 
the whole tail was diffuse, and the posterior portion for fully one-third of the whole visible length 
shewed a convergence inwards. 
But the notable phenomenon is still to come ; allowing the above increase of phase in approach- 
ing perihelion, it is also evident, that if the perihelion distance be very small, the sun may present a 
very large angle as viewed from the comet; and in this way rays of light may reach every part of the 
external coats of the body, and these may be also illumined to that intense degree, that as with the 
sunrise and sunset clouds already referred to, no phase may be seen; so that, with such comets the 
maximum of phase will occur a short distance on either side of the perihelion, at and very close to it 
there will be little or none. Nl 
As the comet of 1843 almost touched the sun’s surface in passing round it, it must have pre- 
sented as satisfactory and conclusive a proof as man could have wished for. But although it must 
have been visible to the naked eye, and to nearly the whole world, in this critical part of its orbit, no 
mortal man is known to have seen it. Rather a melancholy fact of the imperfection of the astrono- 
mical watching of the present age; and it appears all the stronger, from Araco having, in his report 
to the Academy, descriptive of the discovery of a small comet, enlarged on the perfection of the 
system of search organized at the Parisian Observatory ; by which it appeared that nothing could escape 
detection ; for the assistant who made the discovery, having purposely kept silence when he was 
relieved in his watch by another person, this one discovered the same comet before having been an 
hour at his post. But to return to the comet of 1843, it was seen while still not very far from the 
perihelion, when the sun was still subtending a very large angle, viz., on February 28, the perihelion 
passage being February 27, 1843; but then only by three persons, or rather parties, and none of 
them have given sufficiently accurate accounts of what they saw, or have attempted what would have 
been so invaluable, if effectually and faithfully executed, a drawing of the appearances; but their 
statements, as far as they go, decidedly confirm the views above enumerated. The first of these 
happy three, with whose account I became acquainted, was a person at the Cape of Good Hope, who 
(decidedly no scientific person, and having no prejudice in favour of any theory), described the comet 
as he and his shepherd boy saw it at noonday, a bright hazy star, with the hazy matter streaming off 
on one side, and collected into a focus about two feet behind it. Allowing him to have estimated the 
sun’s diameter at one foot, the apparent length of the comet’s tail is well given ; and the comet itself 
being spoken of as a bright star in the hazy matter, which streamed off, and collected into a focus at 
a certain distance behind the head ; this certainly may be interpreted into a somewhat symmetrical 
elliptic figure, having the nucleus in the focus nearest the sun. 
The next testimony is from the ship Owen Glendower, the crew and passengers of which ship, 
when off the Cape on February 28, saw the comet plainly about sunset, “ as a short dagger-like 
object close to the sun.” This is not particularly explicit, but yet we may certainly conclude from 
it, that the comet was broad in the middle of its length, and pointed towards each end, and had 
little or no axial darkness, which sufficiently conforms with our idea of the perfect shape of the 
envelope of a comet seen under such circumstances. 
The last witness is from the United States, where Mr Cruarxe, of Portland, saw the comet at 3° 
p.M., on the same day, and examined it telescopically, and describes it in these words :—“ The 
nucleus, and also every part of the tail, were as well defined as the moon on a clear day. The 
nucleus and tail bore the same appearance, and resembled a perfectly pure white cloud without any 
variation, except a slight change near the head, just sufficient to distinguish the nucleus from the 
tail at that point.” The first sentence well describes the increase of density and definition we have 
already insisted on as a consequence of so near an approach to the sun; and the second paragraph 
as perfectly describes the absence of axial darkness, a consequence partly of the increased brightness 
of the illumination of all the external portion, and partly of its being seen in daylight, and so close 
to the sun; for then, as every one knows, even the darkest shadows amongst the mountains, and in 
the craters of the moon, those which appear absolutely black at night, are, under those circumstances, 
barely distinguishable from the brightest portions. As to the shape, Mr Crarxe says,—that the 

