The Irish standard., 1889-04-13
NEBULE EXPLAINED.

NEBULE EXPLAINED.
Instructive Information for Stu.
dents Of Astronomy.
According TO Late Researches Nebulae Are
Neither Very Distant Clusters of Stars
Nor Masses of Gas, But Merely
Cluster Of Meteorites.
Ptolemy was the first to point out, When
he was making his map of the stars, that
there were certain ''cloudy'' stars, OF which
he gave five on his map, writes j. Norman
Lockyer in Harper's Magazine; and Tycho
Brahe, whose work was done before the in
yention of the telescope, although he did
not notice any bodies which we now class
as nebula, was firmly convinced that that
nebulous luminosity which we call the
Milky Way was something entirely differ
ent in it's nature from the stars. he
imagined it to be what he called an ethereal
essence, a sort Of tre-mist, SO that when In
his time, in the year 1872: d new star al-
peared, he supposed it to be a consloera oAes
ACCOMMODATION Of this ethereal fluid.
Calico was able to show that the Milky
Way. the "ethereal substance Of Tycho.
was only an appearance due to enormous
numbers of stars lying IN the same visual
raw: the stars of which it Is composed can
indeed be seen with very nmall optical
power.
It was not till 1912, a few years after the
introduction OF the telescope, that we goE
the first real definition Of a body which STe
now call a nebula. The first observation
we owe to SIMON Marius, who stated that
some Of the bodies visible in his telescope
exactly resembled the appearance produced
by the flame of 81 candle seen through horH.
II was not till 1866 that the nebula III Ofaor
was discovered, although now to the tfa'nee
eve it is very easily visible, so that 1t seems
rather wonderful that it was not dlscoT~
cred before. In TIA, in England, attenSloE
began to be paid to these bodies, put II IVES
not until the time Of Sir William acrschel
that the most magnificent revelations were
made. He was the first to construct very
large telescopes, by means of which OBJECTS
which appear to the eye as excessively dihos
or objects entirely invisible to the naked
eve. NAV be brought into full visibility. In
this wav Sir William Herschel convinced
birnseH of the existence of a. true nebuloua
fluid differing from stars.
After not only Sir William Hersche], h1t
his son, Sir John Herschel, had &C.
cumulated vast stores OF facts, loro
Rose took up the story, and mads
telescope very much more powerful
than any which had been employed by the
Herschels. His telescope has ght-grasI~
ing power compared with the eye OF 150.:N0
The chief result of Lord Rosse's week yo
which we need here refer is the adea tha5 in
great many bodies which had been classe1
as nebulae this enormous increase OF opsea4
power suggested that VT; were only dealing
with very distant clusters OF stars.
Lord Rose was able 10 get the sug'ges'
ton of s'resolvability" IN SO many bodies
which had been classed as nebulae by Sir
William Herschel and others that gradually
the idea came TO be held that the most neb-
ulous nebula, if we could get sufficient or"
tical power to bear upon it, would be broken
I'D into stars just as certainly as the Milky"
Way had been by Calico.
This would mean that the nebulae were
simply clusters Of stars so Infinitely remote
from our ken that even with the power OF
Lord ROSES Instrument they retained the
appearance Of an ethereal essence.
This was the general opinion Ill lSt4, in
the early days of spectrum analysis, whea Dr.
Higgins turned his spectroscol2e nhe night
to one CT the planetary nebu]as. AT 1rst
he thought that something had gone wrong
in the apparatus, because be could only see
a bright line instead of the usual sort OF
spectrum obtained from a star. Further
work OH other nebulB showed MIN, now
ever. that the spectroscope was doing
it's level best, aud that the cause, the anon
aly, was really that the nebuia gave out
1noncchromatic light, while stars gave out
light of all colors.
In some cases another line was seen, easily
proved to be due to hydrogen, and in another
planetary unebula other observers have
since shown that there is another hydrogen
line visible.
1t became DR., higgins duty to lind out
the origin of the first line observed, and be
came to the conclusion after considerable
labor, that this line was very nearly, it not
exactly, in Che position Of the chief line
seen in the spectrum Of nitrogen, and the
suggestion was therefore made that these
nebulae were masses Of nitrogen and hydro
gen gases mixed, Or if not nitrogen, some
constituent Of nitrogen mixed with hydro-
gen. That result made the idea Of Lord
Rose concerning the possibility of the re-
solvability of nebul@ into stars untenable.
We had to consider from that time that the
light of the nebulB came from q gas or
vapor, and hence it was held thatthe nebula:
were masses Of gas.
Another explanation Of the origin of the
green line has already been given. II we
study the spectrum of magnesium, we flnd
very bright futing With lie less refranGi~
BILE edge absolutely in the position of the
green line; in the nebuae and in comets the
same line appears, not nearly, a,s i'll the eata
Of the line of nitrogen, but absolutely. But
not only so. We find another line of mag
nesium also visible in tho planetary nebulae.
Again, in the spectrum of magnesium burn
ing IN the Bunsen burner can be photo
graphed a line having the exact wave-length
of q line also seen in the nebula Of Orion,
SO that there is considerable amount CT
cumulative evidence chat magnesium is the
true origin Of this spectrum, the luminosity
being produced by meteorites, the chief Con-
stituent Of which is q compound of mag
nesium with oxygen, silicon and iron,
We are therefore justified, until some
better explanation has been given, in hold
ing the view that nebula, like comets, con-
sists Of meteorites, and that they arc Meth
er very distant clusters Of stars nor masses
Of gas.
Cost OF Living in Germany,
The poor of Germany can live much