534 
NATURE 
[ April 5, 1883 
astronomy we have never found a comet's tail really as 
long as this. 
I leave out the detailed description of the comet’s 
aspect, because NATURE has given full accounts and 
sketches, and I come to the most interesting part of M. 
Schiaparelli’s lecture, on the production of those magni- 
ficent phenomena. I translate literally from Signor 
Schiaparelli’s manuscript. 
The proper nucleus of the comet is a solid or liquid 
body so small as rarely to be seen : in the greater number 
of comets, as in this, it seems to be not large enough to 
be visible even in powerful telescopes. It seems also that 
in some comets there are several nuclei, very small and 
close, whose particular atmospheres in their development 
at last unite in one. As long as such a body (or system 
of bodies) remains far from the sun, in extraplanetary 
regions, where temperature is less than — 140° C. (accord- 
ing tothe most moderate estimates),and where the sun has 
perhaps no power to heat it, the matter must be wholly 
solid or at least liquid; and, if a small quantity is 
gaseous or vaporous, it must have a great density and a 
small volume. The progressive approach to the sun by 
its descending orbit will obviously swell the enveloping 
atmosphere, or give rise to one if it does not yet exist, 
with materials generated by the surface. Shortly the 
nucleus begins to appear surrounded by a blaze of light, 
feebleat first, but afterwards more and more brilliant, which 
is the star or head of the comet. Many comets do not go 
beyond this first phase, both because they have not matter 
enough to make an atmosphere, and because they do not 
come near enough to the sun to be subject to a great 
neat. Some comets do not enter the earth’s orbit, others 
cannot reach that of Mars, and we know that the comet 
of 1729 got only a little way into the orbit of Jupiter. 
The most part of those comets, being exposed very 
moderately to the solar influence, cannot increase, and 
remain telescopic ; and it is very probable that a large 
number stop at Jupiter or Saturn’s orbit (or even further) 
in their descent upon the sun: none of those are seen, 
and we can speak of them only by conjecture. 
When a comet, however, as the present, pierces through 
the interior part of the planetary system, it is in the best 
condition to develop its atmosphere if it contain matter 
enough to do so. But the sun, while attracting to him- 
self the nucleus, has the property to repel some of the 
matter of the atmosphere. It is not well known how and 
why this matter is repelled, and to expound the various 
hypotheses on this point would take too long a time. The 
effect of repulsion is nevertheless undoubted, and mani- 
fested by the fact that those parts of the cometary atmo- 
sphere, under the sun’s impulse, almost as if under a gale 
blowing fromit, leave the nucleus and fly in an opposite direc- 
tion away from the sun, producing the tail, which, nourished 
successively by incessant evaporations of the nucleus, 
more and more increases in length, till the atmosphere of 
the nucleus, wholly repelled, overflows into the tail, and 
thus exhausts itself. This happens usually when the 
nucleus, after the perihelion, receding from the sun and 
being then exposed again to the cosmical cold, is no 
longer able to supply with new evaporations the part of 
the atmosphere which the tail absorbs. Deprived thus 
of its former envelopes, and unable to engender others, 
the nucleus is reduced again to itself, and the comet 
disappears. 
The tail of the comet consists then of matters repelled 
by the sun with a mysterious power. But, during the 
above described period of conflagration, other interesting 
events occur in the comet. It is so much swollen and 
convulsed by solar heat that the little nucleus is not able 
sometimes to keep together the fragments by its own very 
feeble attraction. Violent eruptions take place at the 
surface, so that pieces of nucleus are raised and thrown 
out of the principal body’s attraction. Those fragments 
then pass through the heavens as independent bodies, 
and their orbits are not very different from the orbit of the 
nucleus. Sometimes one of the broken pieces is great 
enough to engender another separate comet: that is, the 
several times observed phenomenon of a divided comet. 
But most generally it seems that separated pieces are 
very small and numerous, like the sparks of a piece of 
salt thrown on the fire; and extend along the trajectory 
of the nucleus like a current or projection of corpuscles, 
which gradually invade all the orbit of the comet. Many 
comets (probably all) engender in their course a similar 
retinue ; and the planetary intervals are peopled by those 
corpuscles produced by a comet’s partial disintegration. 
When the earth in its yearly revolution passes through 
one of these processions it meets with several pieces, 
which get inflamed by contact with the terrestrial atmo- 
sphere, and burn in a very short time, producing a falling 
star. 
An example of such a process of separation was given 
by the present comet. In effect, a little before Octcber 15 
M. Schmidt, the astronomer at Athens, observed an irre- 
gular and very feebly shining thin cloud leaving the 
comet, withdrawing, and finally disappearing. It was more 
dense and luminous in some places than in others, but it 
looked not like a comet, having rather the aspect of a 
mass of corpuscles exploded by the principal nucleus. 
The atmosphere also enveloping the principal nucleus 
offered analogous phenomena, being not round and sym- 
metrical, but lengthened spindle-fashion, with several 
more luminous centres of different intensity spread in an 
oval cloud. We have, besides, reason to believe that 
another little comet, which was observed in the beginning 
of 1880 in the austral regions of the earth, running in an 
orbit very similar, was previously separated from our 
great comet. 
M. Schiaparelli passed afterwards to another question, 
on the chemical constitution ef comets, explaining the 
principle of spectrum analysis and its application to 
celestial chemistry. He remarked that the present and 
Wells’s comet only, by their coming so near the sun, 
could present the lines of sodium, whilst all the comets 
before observed gave only lines of hydrocarbons in the 
spectroscope; and it is very probable, according to 
modern theories, that comets contain also some matters 
which are made apparent in falling stars and in aérolites, 
as iron, nickel, silicium, magnesium, aluminium, and 
others. This confirms the induction as to the similarity of 
their chemical composition to that of the earth; and the 
common origin of comets in the planetary system is evi- 
dently proved by their accompanying the sun in its pro- 
gressive movement towards the constellation of Hercules. 
It seems that comets belonging to the solar system would 
have the function of continually dissipating matter in 
space, as a compensation to the attractive power of the 
greatest centre, the sun. 
Pressure of space obliges me to leave out the very 
eloquent conclusion of this lecture, in which the lecturer 
refuted the apprehensions as to the shock of a comet with 
the earth, and its probable consequences, discussing the 
great moral importance of these studies as an antidote to 
the fears and superstitions of ignorant people. Referring 
to Anaxagoras and Galileo, he concluded with these words: 
“© A science which suffered such noble condemnations, 
| and is able to awake such noble hopes, cannot be con- 
sidered as futile and idle; it will always be dear to the 
friends of truth; dear to every one who is convinced that 
man lives not by bread alone.” FRANCIS PORRO 
R. Observatory of Brera in Milan 
THE SOARING OF BIRDS 
ete recent correspondence in NATURE upon this 
subject ought not to close without some reference 
to a possible explanation of soaring which does not appear 
to have been yet suggested. 
