APPENDIX NO.I.
[*75] , [*76] and [*77]

THE INSTANCE OF THE DOUBLE STAR
95 HERCULIS, AND ITS MARKED
VARIATIONS IN COLOUR
COMPLETELY PROVED.

Prelude.

As this object constitutes a remarkable case of Sidereal Chromatics, in which Nature seems to have been caught at her work, some account of the decided mutations of colour recently detected in it becomes necessary; and the story may be related in a few words. It should, however, be premised that we are told (and it is highly probable), that light, when first emitted from the photospheres of the sun and stars “should be in all eases identical, the differences of colour depending upon the differences of constitution of the investing atmosphere :” but the variability of the hues in question is still to be explained, since they cannot be satisfactorily accounted for by any prevailing scientific theory. It is truly wonderful; and at the present statics of the phenomenon, we can only ejaculate St. Augustine’s rem vidi, cansam non vidi.
Still it behoves us, like humble neophytes, not merely to wonder and worship, for that line of conduct would not advance us in the adoration due to our omniscient and omnipresent CREATOR. We must endeavour to understand the glorious phenomena so benignantly opened out to us as portions of a vast design. Some features of nature may be more important for our comprehension than others, yet in our present nescience we should patiently regard them all with equal care, and scrutinise them until their apparent Mystery is unveiled. When that happy consummation may occur, it is not for us to anticipate; but in the meantime we recommend the path we have advocated, to be trod with zeal commensurate with the object. An evident change of brightness or of colour, in a sidereal system, may indicate a long period; but it may also prove a chain of pulsations, which, if apparently irregular to the inexperienced, may finally prove to be regularly irregular. [*78]
At page 35 of this little work', it is mentioned that my son, Charles Piazzi Smyth, made his observations on the colours of the components of 95 Herculis in the year 1856, under impressions which occasioned much surprize to myself and others. At length in the autumn of 1862, he, being on a visit to James W. Grant, Esq. of Elchies, on the banks of the Spey, took the opportunity of efficiently re-observing - among others - the pair before us with that gentleman's fine equatorially-mounted refracting telescopes of no less than 11 inches aperture. The following are the conclusions arrived at by the interesting scrutiny; but to a general reader it may be necessary to explain that, under the heading.”
“Authority,” σ means Struve using a small instrument and Σ. the same gentleman with the Dorpat 9-inch; “Cycle” and “Spec. Hare.” are from my observations, and “Guajara” and “Elchies” are those of J. P. Smyth:-

95 HERCULIS. Approx. R.A. - 17h 55m 33;
Decl. +21° 35' 56" for Jan. 1, 1860.

Registered colours.

Remarks by C. P. Smyth. [*79]

“The magnitudes may vary through half a magnitude.
“The colours vary astonishingly; and, as one of the most; remarkable cases in the heavens, may be treated at length. On my return from Teneriffe I had communicated the observed colours of this, amongst a series of other stars, to my father and his friends, and they seized on my equality of the colours of the two components of 95 Herculis, as one great anomaly in my list, and chief divergence from the Cycle, where they are extremely contrasted; and, several observers being called together the next summer, they proved unanimously that the Cycle was right. I remained, however, positive that I had observed the alleged equality, and on two nights; for, being surprised, and in a manner amazed at it, having promised on the strength of the printed description to show a bystander a case of remarkably contrasted coloured to try to perceive some approach to them; but, though certain strange flickerings of colour appeared on one of the nights, there was nothing to disturb the general equality of the two discs, and their close approach to white, or a light neutral grey.

Its real changes of hue.

“All this tinge it is true that Sestini's observation of 1844 was on record, I, renouncing both the stars gold - yellow, but; it was not until recently referring to Struves original observations, which are partly given above, that I became convinced of this being a pair of cosmical and brilliant changers of colour; A passing

from yellow
to greyish, from that
to yellowish with blue tinge, from that
to greenish, from that
to light green, from that
to light apple green, from that
to "astonishing yellow green," and from that
to yellow again.

“in a period of probably twelve years, while B in the same time passes

from yellow
to greyish, from that
to yellowish with reddish tinge, from that
to reddish, from that
to cherry red, from that
to “egregious red” and from that
to yellow again.

“Real [*80] physical changes, these in each star, there can be no doubt; though in this case the one colour is so generally the complement of the other, a case will be found farther on where one component of a double star goes through brilliant periodic changes of colour, without the other component very sensibly altering its tint? [16]

Is it a binary system?

“In position and distance ‘fixity’ and an optical character have hitherto been both assigned and confirmed to 95 Herculis; but now, with the assistance of the Elchies observation and the B.A.C-proper motion, which, does not make its appearance relatively between the two components, I have the utmost confidence to declaring the pair to be binary, and undergoing a slow retrograde movement in angle, of about 2^o in forty years, roughly - a conclusion which, though it must prove fruitless for ages in enabling the orbit to be approximated to, is nevertheless of vital consequence in studying the strange chromatic problems which the stars present.”

Notice from Bedford.

While the above exposition was being prepared for the press, the changes of hue in 95 as been noticed been entirely independently at Bedford, by Captain John Huggins, who favoured me with the details before he could have possibly heard of the operations at Elchies. His statement is printed in the “Monthly Notices” of the Royal Society for November 1868, from which publication it is here extracted.

On the Colours of the two Components Stars of 95 Herculis.

Mr. Higgens, in a letter dated Bedford, 17th April 1863, addressed to Admiral Smyth, writes as follows:

“I beg to forward a few notes on 95 Herculis.
“When I last saw the star, in the autumn in of last year, the colours were as noticed in the Cycle; A, apple-green; B cherry red.
“I first saw it this year on the 23rd April, but the bright hues were not there, and greenish-white and pinkish-white were all I could affirm.

“May 10th. Hues more faint. I could only record them as dull white, both A and B.[*81]

95 Herculis

“Aug. 1st. A, greenish-white; B, yellowish: both changing lightly till 95 Herculis. Aug. 12, when they showed as in tile Cycle; A, apple-green; B, cherry-red. A first shewed signs of deepening colour, the hues becoming more apparent every night, B changing from yellow to red more rapidly.
“It was not possible to note night by night the amount of change; but it was very palpable after an interval of three or four nights, and continued so till both stars showed their normal colours.
“The instruments used were, a 3¼-inch achromatic with 80, and a 4-inch with 115; both glasses by Cooke, of York.”

Admiral Smyth remarks:

“The star in question, 95 Herculis, is now a crucial instance of sidereal colour-changing; and it has given some little trouble, both to my son Piazzi and myself already, in poring over the registered observations.
“It is to be hoped that a field of research at once so elegant, easy, and useful, will be followed up by some of those Fellows of the Society who possess both means and leisure to pursue the interesting inquiry.”
“The Astronomer Royal, however, suggested to Admiral Smyth that the simultaneous change for the two stars is suspicious, and looks like a possible change in the telescope.”

Epoch of 1864.

Captain Higgens continued his watch over this object, during the apparition of the present year with commendable perseverance; and 1864 on the 10th of August wrote thus:-

“I beg to forward the results of thirty-eight observations of 95 Herculis, made on different days from May 21st to August 8th, with Cooke’s achromatic telescope of 4-inches aperture and 5-feet focus, under powers 115 and 200.
“Of the thirty-eight observations eight are noted as simply normal, nineteen as showing A fainter than last year when in full normal coloured and eleven as showing both A and B fainter; and my impression is, that they are not so vivid as they were last September, and that A shows more loss colour than B, though neither to the extent of justifying their being classed as anything but normal, though somewhat faintish.
"It hits always struck me that the definition of their colours in the Cycle, a slight apple-green and cherry-red, is the most graphical description that could he applied to these beautiful objects. I have watched then with great care and interest, from having had the good fortune last year of detecting the change of colour from white to their normal condition, as reported to you.”

On the 11th the Captain informed me, “I received a letter from the Rev. Mr. Webb this morning, in which he incidentally mentions 95 Herculis as follows:- ‘I fancied the other night the red decidedly more marked than the green.’ Now, as I had not mentioned to him that I have been engaged in observing 95 Herculis this year, I feel pleased at so independent a confirmation of my notation A (green) being fainter than usual.”

ENDNOTES

[16] This alludes to the most interesting 70 Ophiuchi, the B of which my son assumes to vary through a variety of colours, at periods yet unascertained; and that yellow, green, violet, purple and red, are permanently registered. But from many conditions of the case, I am persuaded we must await more observations before conclusions can become at all satisfactory.

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