ARTICLE PAGESAPPENDIX NO.II. [*82]THE COLOURS OF DOUBLE STARS
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Star | Components | Magnitude | European Colour | Teneriffe and Indian Colour |
113 P. Ceti | A | 7 | Yellow | Strong yellow |
B | 9 | Blue | Warm grey | |
146 P. Ceti | A | 6.5 | Yellow | Yellow |
B | 9 | Violet | Pale violet | |
32 Eridani | A | 5 | Orange | Orange |
B | 7 | Greenish | Greenish | |
5 Aquilæ | A | 7 | White | Pale yellow |
B | 8 | Blue lilac | Bluish | |
ψ1 Aquarii | A | 4 | Orange yellow | Cadmium Yellow |
B | 4.5 | Blue | Blue |
Star | Components | Magnitude | European Colour | Teneriffe and Indian Colour |
ν Serpentis | A | 4.5 | Greenish | Bluish |
B | 9.0 | Coppery | Warm blue | |
185 P. Antinoi | A | 9 | Yellow | White |
B | 10 | Blue | White | |
C | 12 | Violet | Blue | |
186 P. Antinoi | A | 7.5 | Whitish | Yellow |
B | 9 | Blue | Blue | |
α2 Capricorni | A | 3 | Yellow | Yellow |
B | 16 | Blue | Blue | |
τ1 Aquarii | A | 6 | White | Light yellow |
B | 9.5 | Violet | Pale violet | |
94 Aquarii | A | 6 | Orange | Yellowish |
B | 8.5 | Faint lilac | Greenish blue | |
107 Aquarii | A | 6 | White | Pale yellow |
B | 7.5 | Bluish | White |
Star | Components | Magnitude | European Colour | Teneriffe and Indian Colour |
α Scorpii | A | 1 | Fiery red | Orange red |
B | 11 | Emerald | Pure blue | |
39 Ophiuchi | A | 5.0 | Orange | Pale yellow |
B | 7.5 | Bluish | Faint blue | |
α2 Piscis Austr. | A | 1 | Reddish | White |
B | 9.5 | Dusky blue | Blue |
Atmospheric effects perceptible.
“Now, from the first of these lists, it would appear that all its five pairs of stars are coloured to European, almost precisely as to more southern, observers; and that, in so far, European observations of colour are quite safe down to 10 degrees below the celestial equator. [*85] But in the second list, or from 10 to 20 degrees below the equator, three out of its seven stars show unmistakable symptoms of atmospheric colouration — yellowish being changed into orange, bluish into greenish, and white into blue. While in the third list, or from 20° to 30° south declination, every star there shows, and in each of its components, the same effect to an increased degree — white being turned into reddish, pale yellow into orange, orange red into fiery red, and pure blue into bluish green, or dusky blue, as depending doubtless on variations of the lower atmosphere at the several times of observation.
Safe limits for colour observations on stars.
“Hence there can be hardly a doubt
but that, in the important physical question of the real colours of
stars, no European observations should be received below the
fifteenth degree of south declination; and that, if powerful spectrum
analysis be employed, the range should not exceed the fifth degree,
or just so far beyond the equator as may give a southern observatory,
attending to the southern stars, a few common objects of observation
for index differences.
“Meanwhile, with regard to the
Teneriffe and Elchies stars, it is most satisfactory to find, after
throwing out; the cases of atmospheric disturbance, that the rest
are, on the whole, so very trustworthy and similar to both the ‘Cycle’ and F.
W. Struve’s colours, that, if a case of
particular divergence be therein found, it is capable of being
referred to a physical change of the stars real colour; almost
as confidently indeed as an eye observation of change of brightness
may be assigned to a real change of ‘magnitude;’
and, consequently, renders the exact date of the chromatic
phenomenon, necessary accompaniments to its description.” [*86]
On Nebulae.
ALTHOUGH the cause is utterly unknown, and in the present stage
of human cognoscence appears to be inscrutable, it is surmised that
the exceptional bodies designated Nebulæ have a connection
with double-stars (see Arago’s
Popular Astronomy, book xi. chapter xxiv.) while, as to colours,
I have noticed in them pale tints of white, creamy white, yellow,
green, and blue. It therefore follows that these incomprehensible
but palpable evidences of Omnipotent power and design are not
unnecessarily hauled in and appended to our dissertation upon
Sidereal Chromatics.
It will be recollected by all who are really concerned about tile
matter, that, when the wondrous revelations of Lord Rosse were
communicated to the public, certain buzzing popinjays, who hang
about, and obstruct the avenues to the temple of science,
vociferously proclaimed that the Nebular Theory had received its
coup de grace from the castle at Parsonstown. Now this crude conceit
was assuredly not imbibed from his Lordship’s statement, he having most pointedly said,
that “now, is as has always been the
case, an increase of instrumental power has added to the number of
clusters at the expense of the nebulæ properly so called;
still it would be very unsafe to conclude that such will always be
the case, and thence to draw the obvious inference that all
nebulosity is but the glare of stars too remote to be separated by
tile utmost power of our instruments.”
In the Speculum Harlwellianztm
(pages 111-114) I gave my fully considered opinion on this head,
showing tile actual state of the question, and advocating that
planetary nebulæ diffuse patches of we know not what emanating
light, arm all the “island
universes” so profusely scattered in
the abysses of space, should be competently watched for ages. Now
those “Thoughts on the Nebular
Hypothesis” were written in the year
1860, as an addendum to what I had already published on the same
subject in my Cycle of Celestial Objects. It was therefore
with pleasure, while this, the last sheet, is passing through the
press, that I received a letter from my [*87] unflagging friend Mr. William Huggins,
in which he thus announces the conclusion arrived at front the
masterly experiments lately made at Tulse Hill: “I fancy you will be interested in the
result of some observations I have recently made on the spectra
of some of the nebulæ. I have obtained evidence, which I
believe will be accepted as satisfactory, that certain of the
nebulæ(at present my list contains five PLANETARY nebulæ
and the annular one in Lyra) are certainly, NOT clusters
of stars. They are probably enormous masses of glaiding or
ammoniacal gas containing comparatively small quantities of matter
condensed into the liquid or solid state. The observations are now
at the printer’s, and I hope within a
fortnight to send you a copy of them. After the opinions which you
have published, thinking you must be greatly interested in the
matter, I have ventured to trouble you with this note in
anticipation.”
So enchanting a vista of successive discoveries has or late been
thrown open to us, through following up the long-neglected
unravelling properties of the Prism, and applying the delicate yet
unequivocal test to the heavenly bodies. that a few familiar
explanations of the spectra of so experienced a hand as Mr. Huggins
may be acceptable to many an amateur-gazer who is now endeavouring
on fine nights to interpret those brilliants. In expounding the
subject, he thus popularly expresses himself:-
Mr. Huggin’s explanation.
“The dark spaces due to
interference are supposed to be produced by the action of light upon
light- but the dark lines of the spectrum by the absorptive action
of vapours or gases upon light. In the ease of interference
according to the undulatory theory, when two waves of homogeneous
light from the same source, and proceeding by two different routes a
little unequal in length, meet in opposite phases of an undulation,
they destroy each other’s motion, and
so there results a calm in the luminiferous ether. When no waves
dash upon the retina, the eye is without stimulus, and this calm we
call darkness.
“The present theory of the nature and
origin of the dark lines of the solar spectrum is quite recent. In
1855 Balfour Stewart published a paper on the law of exchanges in
radiant heat. In the following year the subject was taken up by
Kirchoff, who extended the theory to light. The conclusion at
which he arrived may be thus stated :- When any substance is heated
or is rendered luminous, rays of certain and definite degrees of
refrangibility are given out by it, whilst the same substance has
also the power of absorbing rays or these identical
refrangibilities. Thus the light of burning sodium or glaiding,
sodium vapour, cannot get through the vapour of sodium, though this
vapour is wholly powerless to absorb or quench light of any
refrangibility other than that which sodium vapour emits when heated
till it is luminous. In this way the double line D of the solar
spectrum can be experimental produced.
“How is light absorbed by gas or vapour? The
theory is as follows:- The atoms [*88]
of a gas being freer to move than those of a liquid or a
solid, are capable of swinging or vibrating at certain definite
rates only. These atoms have also the power of intercepting the
waves which were excited by atoms swinging at the same rates, and
these only. Thus atoms, the motions of which are suitable for the
emission of red light, will stop red light, and so on. [17]
“The maps accompanying my paper show
the several distinct rates or vibration corresponding to the motions
of the gaseous atoms of the elements described. Each line by its
place in the spectrum indicates a definite wave-length, just as each
note of a piece of music indicates a definite rate of vibration of
the air. These maps may be termed the light-songs or the elements
written down in notes. Absorption is therefore according to this
theory a transference of motion from the ether to the material
particles immersed in it.
“Thus it appears when the light
emitted from the solid or liquid photosphere of the sun has to
traverse its atmosphere, crowded with vapours of different
substances, each vapour stops its own group of lines of light, and
so the original light reaches us lessened by the aggregate of all
the groups of all the vapours. Now, when this light is spread out by
the prism, the dark doings of these vapours are revealed, and dark
lines or dark spaces show the places where tile light has been
intercepted.”
Chemical substances.
Such are the reasonable expectations of observational and experimental science, as connected with the constitution of those substances which optical analysis afforded the means of discovering in the heavenly bodies. A reading of Mr. Huggins's statement to the Royal Society on the “Spectra of some of the Chemical Elements” will show the care and labour involved in constructing the Spectroscope apparatus with which he scrutinized gold, silver, thallium, cadmium, lead, tin, bismuth, antimony, potassium, arsenic, palladium, lithium, strontium, platinum, tellurium, osmium, rhodium, iridium, manganese, chromium, cobalt, nickel, and iron. In fine: if the pestilent earth-annihilating prophets who have recently frightened some old women, of both sexes, out of their wits, will but permit our globe to roll noiselessly on its axis for another century astronomy will be found in possession of many realities which, in 1864, are only to be classed among the numerous desiderata of Uranology.
β Cygni
In employing various eyes and instruments upon this fine double β Cygni star, I was, of course, desirous of securing the evidence afforded by the powerful achromatic telescope at Greenwich. But; it was only as this sheet is being concluded — considerably after the eleventh hour — that I received the reply; yet it is of that; interest to the question, that I here append it as received.
Royal Observatory, Greenwich, London,
8.E.
1864, September 29, evening.
Mr Dear
Sir,
Various circumstances have impeded the examination of
β Cygni, but; here I send it at
last. You may depend upon the result as accurately; it has been
carefully referred to an accurate standard.
I give it, on the
other leaf, in the words in which it was given to me.
I am, my dear Sir,
Yours most
truly,
G. B. AIRY. Admiral W. H.
Smyth.
Observations by Mr. J. Carpenter.
“The large star is bright yellow,
about the colour of that part of the solar spectrum situate at a
point about one-eighth of the distance between Frauenhofer’s D and E, reckoning from D towards E.
(Sensibly the same colour as the flame of a hand-lamp fed with Colza
oil).
“The small star is pale
blue, about the colour of that part of the spectrum which is crossed
by the F. (Sometimes it was suspected that the light of this star
had a slightly greenish tinge.)
“These comparisons were made on two
evenings with a drawing of the spectrum by M. Chevreul, in his ‘Exposè d’un, Moyen de
dèfinir et de nommer les Couleurs,’ and this drawing was afterwards compared
with the solar spectrum itself at the points used for the star
comparisons, and was found to be accurate.
“When the eye-piece was pushed within
the proper focus, the contrast between the colours of the discs
seemed more striking than when the proper focus was used; and, when
the eye-piece was pulled out beyond the proper focus, the
contrast seemed less striking.
“The colours were most strongly
contrasted with low powers, as they were also when the image was
viewed without any eye-piece. With higher powers the colours became
a little more nearly similar, the yellow star seeming to retain its
colour, but the blue becoming a little yellowish in its centre.”
The ending.
One word in conclusion. With all my admiration of the marvellous and extensive power of Chemistry in disintegrating the nature and properties of the elements of matter, I really trust it will not be exerted among the Celestials to the disservice or detriment of measuring agency; and this I hope for the absolute maintenance of GEOMETRY, DYNAMICS, and pure ASTRONOMY.
[17] “When two waves meet in the relative position shown in No. 1 in consequence of the opposite direction of their motion they are both destroyed. But when two
waves meet in the relative position shown in
No. 2, they co-operate, and there is a double amount of
light.
See also Professor Tyndall on “Heat as a mode of Motion.”
Last Update : 26th April 2017
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