[1] _The Observatory_, Nos. 231-234, 1895.
[2] _Observations of Comets_, translated from the Chinese _Annals_ by
John Williams, F.S.A. (1871).
[3] J.L.E. Dreyer, _Proc. Roy. Irish Acad._ vol. iii. No. 7 (December
1881).
[4] F.K. Ginzel, "Die astronomischen Kenntnisse der Babylonier," C.F.
Lehmann, _Beitrage zur alten Geschichte_, Heft i. p. 6 (1901).
[5] _Knowledge and Scientific News_, vol. i. pp. 2, 228.
[6] _Astronomisches aus Babylon_ (Freiburg im Breisgau, 1889).
[7] Ginzel, loc. cit. Heft ii. p. 204.
[8] _Die babylonische Mondrechnung_, p. 50 (1900).
[9] S. Newcomb, _Astr. Nach._ No. 3682; P.H. Cowell, _Month. Notices
Roy. Astr. Soc._ lxv. 867.
[10] G.V. Schiaparelli, _I Precursori del Copernico_, pp. 23-28,
Pubbl. del R. Osservatorio di Brera, No. iii. (1873).
[11] G.V. Schiaparelli, _I Precursori del Copernico_, pp. 23-28,
Pubbl. del R. Osservatorio di Brera, No. ix.
[12] Marie. _Hist. des sciences_, t. i. p. 79; P. Tannery, _Hist. de
l'astronomie ancienne_, ch. v. p. 115.
[13] Published by H.C. Schjellerup in a French translation (St
Petersburg, 1874).
[14] Newcomb, _Researches on the Motion of the Moon_, Washington
Observations for 1875, Appendix ii. p. 20.
[15] F. Baily, _Memoirs Roy. Astr. Society_, vol. xiii. p. 19.
[16] J.L.E. Dreyer, _Life of Tycho Brahe_, p. 321.
ASTROPALIA (classical _Astypalaea_), an island, with good harbours, in
the south part of the Aegean, situated in 36.5 deg. N. and immediately
west of 26.5 deg. E. It was colonized by Megara, and its constitution
and buildings are known from numerous inscriptions. The Roman emperors
recognized it as a free state, and in the middle ages it was called
_Stampalia_, and belonged to the noble Venetian family of Quirini. It
was taken by the Turks in the 16th century, and is now noted for its
sponges. The customs and dress of the people, who speak a patois of
romaic origin, are interesting.
ASTROPHYSICS, the branch of astronomical science which treats of the
physical constitution of the heavenly bodies. So long as these bodies
could be known to men only as points or disks of light in the sky, no
such science was possible. Even later, when the telescope was the only
instrument of research, knowledge on this subject was confined to the
appearances presented by the planets, supplemented by more or less
probable inferences as to the nature of their surfaces. When, in the
third quarter of the 19th century, spectrum analysis was applied to the
light coming to us from the heavenly bodies, a new era in astronomical
science was opened up of such importance that the body of knowledge
revealed by this method has sometimes been termed the "new astronomy."
The development of the method has been greatly assisted by photography,
while the application of photometric measurements has been a powerful
auxiliary in the work. It has thus come about that astrophysics owes its
recent development, and its recognition as a distinct branch of
astronomical science, to the combination of the processes involved in
the three arts of spectroscopy, photography and photometry. The most
general conclusions reached by this combination may be summed up as
follows:--
1. The heavenly bodies are composed of like matter with that which we
find to make up our globe. The sun and stars are found to contain the
more important elements with which chemistry has made us acquainted.
Iron, calcium and hydrogen may be especially mentioned as three familiar
chemical elements which enter largely into the constitution of all the
matter of the heavens. It would be going too far to say that all the
elements known to us exist in the sun or the stars; nor is the question
whether the rarer ones can or cannot be found there of prime importance.
The general fact of identity in the main constituents is the one of most
fundamental importance. It would be going too far in the other direction
to claim that all the elements which compose the heavenly bodies are
found on the earth. There are many lines in the spectra of the stars, as
well as of the nebulae, which are not certainly identified with those
belonging to any elements known to our chemistry. The recent discoveries
growing out of the investigation of newly discovered forms of radiation
lead to the conclusion that the question of the forms of matter in the
stars has far wider range than the simple question whether any given
element is or is not found outside our earth. The question is rather
that of the infinity of forms that matter may assume, including that
most attenuated form found in the nebulae, which seem to be composed of
matter more refined than even the atoms supposed to make up the matter
around us.
2. The second conclusion is that, as a general rule, the incandescent
heavenly bodies are not masses of solid or liquid matter as formerly
assumed, but mainly masses either of gas, or of substances gaseous in
their nature, so compressed by the gravitation of their superincumbent
parts toward a common centre that their properties combine those of the
three forms of matter known to us. We have strong reason to believe that
even the sun, though much denser than the general average of the stars,
may possibly be characterized as gaseous rather than solid.
Probabilities also seem to favour the view that this may, to a certain
extent, be true of the four great planets of our system. The case of
bodies like our earth and Mars, which are solid either superficially or
throughout, is probably confined to the smaller bodies of the universe.
3. A third characteristic which seems to belong to the great bodies of
the universe is the very high temperature of their interior. With a
modification to be mentioned presently, we may regard them as intensely
hot bodies, probably at a temperature higher than any we can produce by
artificial means, of which the superficial portions have cooled off by
radiation into space. A modification in this proposition which may
hereafter be accepted involves an extension of our ideas of temperature,
and leads us to regard the interior heat of the heavenly bodies as due
to a form of molecular activity similar to that of which radium affords
so remarkable an instance. This modification certainly avoids many
difficulties connected with the question of the interior heat of the
earth, sun, Jupiter and probably all the larger heavenly bodies.
A limit is placed on our knowledge of astrophysics which, up to the
present time, we have found no means of overstepping. This is imposed
upon us by the fact that it is only when matter is in a gaseous form
that the spectroscope can give us certain knowledge as to its physical
condition. So long as bodies are in the solid state the light which they
emit, though different in different substances, has no characteristic so
precisely marked that detailed conclusions can be drawn as to the nature
of the substance emitting it. Even in a liquid form, the spectrum of any
kind of matter is less characteristic than that of gas. Moreover, a
gaseous body of uniform temperature, and so dense as to be
non-transparent, does not radiate the characteristic spectrum of the gas
of which it is composed. Precise conclusions are possible only when a
gaseous body is transparent through and through, so that the gas emits
its characteristic rays--or when the rays from an incandescent body of
any kind pass through a gaseous envelope at a temperature lower than
that of the body itself. In this case the revelations of the
spectroscope relate only to the constitution of the gaseous envelope,
and not to the body below the envelope, from which the light emanates.
The outcome of this drawback is that our knowledge of the chemical
constitution of the stars and planets is still confined to their
atmospheres, and that conclusions as to the constitution of the interior
masses which form them must be drawn by other methods than the
spectroscopic one.
When the spectroscope was first applied in astronomy, it was hoped that
the light reflected from living matter might be found to possess some
property different from that found in light reflected from non-living
matter, and that we might thus detect the presence of life on the
surface of a planet by a study of its spectrum; but no hope of this kind
has so far been realized.
We have, in this brief view of the subject, referred mainly to the
results of spectrum analysis. Growing out of, but beyond this method is
the beginning of a great branch of research which may ultimately explain
many heretofore enigmatical phenomena of nature. The discovery of
radio-activity may, by explaining the interior heat of the great bodies
of the universe, solve a difficulty which since the middle of the 19th
century has been discussed by physicists and geologists--that of
reconciling the long duration which geologists claim for the crust of
the earth with the period during which physicists have deemed it
possible that the sun should have radiated heat. Evidence is also
accumulating to show that the sun and stars are radio-active bodies, and
that emanations proceeding from the sun, and reaching the earth, have
important relations to the phenomena of Terrestrial Magnetism and the
Aurora.
The subject of Astrophysics does not admit of so definite a subdivision
as that of Astrometry. The conclusions which researches relating to it
have so far reached are treated in the articles STAR; SUN; COMET;
NEBULA; AURORA POLARIS, &c. (S. N.)
ASTRUC, JEAN (1684-1766), French physician and Biblical critic, was born
on the 19th of March 1684 at Sauve, in Languedoc. He graduated in
medicine at Montpellier in 1703, and in 1710 he was appointed to the
chair of anatomy at Toulouse, which he retained till 1717, when he
became professor of medicine at Montpellier. Subsequently he was
appointed successively superintendent of the mineral waters of Languedoc
(1721), first physician to the king of Poland (1729), and regius
professor of medicine at Paris (1731). He died on the 5th of May 1766 at
Paris. Of his numerous works, that on which his fame principally rests
is the treatise entitled _De Morbis Venereis libri sex_, 1736. In
addition to other medical works he published anonymously _Conjectures
sur les memoires originaux dont il parait que Moyse s'est servi pour
composer le livre de la Genese_, (1753), in which he pointed out that
two main sources can be traced in the book of Genesis; and two
dissertations on the immateriality and immortality of the soul, 1755.
See Hauck, _Realencyk. f. prot. Theol._, 1897, vol. ii. pp. 162-170.
ASTURA, formerly an island, now a peninsula, on the coast of Latium,
Italy, 7 m. S.E. of Antium, at the S.E. extremity of the Bay of Antium.
The name also belongs to the river which flowed into the sea immediately
to the S.E., at the mouth of which there was, according to Strabo, an
anchorage. The medieval castle of the Frangipani, in which Conradin of
Swabia vainly sought refuge after the battle of Tagliacozza in 1268, is
built upon the foundations of a very large villa, of _opus reticulatum_
with later additions in brickwork, and with a small harbour attached to
it on the south-east. Remains of buildings also exist behind the sand
dunes, which possibly mark the line of the channel which separated the
island from the mainland, and these may have belonged to the
post-station on the Via Severiana. As far as can be seen at present,
there are remains of only one villa on the island itself;[1] but along
the coast a mile to the north-west a line of villas begins, which
continues as far as Antium. To the south-east, on the other hand,
remains are almost entirely absent, and this portion of the coast seems
to have been as sparsely populated in Roman times as it is now. The
island seems to have existed as such in the time of Pope Honorius III.
Astura was the site of a favourite villa of Cicero, whither he retired
on the death of his daughter Tullia in 453 B.C. It appears to have been
unhealthy even in Roman times; according to Suetonius, both Augustus and
Tiberius contracted here the illnesses which proved fatal to them.
See T. Ashby, in _Melanges de l'Ecole Francaise de Rome_ (1905), p.
207. (T. As.)