371 XXVIII.—On the great Refracting Telescope at Elchies, in Morayshire, and its Powers in Sidereal Observation. By Professor C. PIAZZI SMYTH. (Read December 1862 and March 1863.) PART-A.—INSTRUMENTAL DETAILS, ..... Pages 371-380 PART B.—OBSERVATIONAL PARTICULARS, .... 380-413 PART C—GENERAL DEDUCTIONS, ..... 413-418 PART A.—1. Introduction to Instrumental Details. The following pages contain an account of a few double-star measures which, by the kind permission of J. W. GRANT, Esq., of Elchies, in Morayshire, I was enabled to make there in September 1862, with his large and equatorially mounted refracting telescope; and as that instrument is altogether the best and most powerful of its kind which has hitherto been erected in Scotland, such a trial of its capabilities, and the first which has been published, will undoubtedly have a peculiar interest for the Royal Society of Edinburgh. The object-glass of the telescope is 11 inches in diameter, or rather its clear aperture, for the glass discs themselves may be a little more; while the next largest in Scotland, that recently acquired by the Glasgow Observatory, under its present able director, Professor GRANT, is not more than 9 inches; and the chief object-glass of the Royal Observatory of Edinburgh, or that of the Meridian Transit Instrument, only Q\ inches aperture. The light, therefore, of the Elchies telescope is, comparatively,* transcendent; and to enable this feature to be em- ployed with the best effect upon his favourite stellar pursuits of earlier years in India, where extreme accuracy of measurement was always one of his chief desiderata, Mr GRANT spared no expense in securing for the Elchies instru- ment an unusually efficient and well made equatorial mounting, fully provided with clockwork motion and micrometrical apparatus. The order for the construction of this instrument would appear to have been given about the year 1849, a period when Mr GRANT, though still in India, was just about to bring to a close his long service of forty-four years of continued official residence there: and it seems to have been commenced immediately; * It would not be right to ignore that both England and Ireland have object-glasses of 12 inches in diameter ; that the Russian Observatory of Pulkova has possessed for a quarter of a century, and used with great profit to exact astronomy, an object-glass of 15 inches in diameter; and that, in addition to Paris, the astronomers of the United States have now in employment one of the same size, and also one even of 18 inches in diameter, the normal size for a new generation, with similar advantageous results. VOL. XXIII. PART II. 5 I 372 PROFESSOR C. PIAZZI SMYTH ON THE for, in 1851, the equatorial mounting, in its chief parts, was exhibited by Mr ANDREW EOSS, the optician employed, as his so-called "trophy" in the eastern half of the Nave of the Great Exhibition building of that year, with the effect of gaining for him one of the highest medals awarded. But after that event, lamentable delays took place in finishing the instrument; and before they were all concluded, Mr GRANT'S health, too long tried by an Indian climate, unhappily broke down altogether. Hence it eventually occurred, that this fine instrument,— with the assistance of which, as the character of the work he had already exe- cuted in India with a smaller telescope sufficiently demonstrates, its owner would soon have risen to the first rank of acknowledged double-star observers in this country,—remained nearly unused until my going to Elchies in September 1862. I had only intended on that occasion to pay a passing visit, as one of respect to the founder of the largest astronomical equatorial in Scotland; but Mr GRANT'S hospitable notions, and his ideas of the importance of anything at all promising to be useful in practical astronomy, prevented my quitting his mansion until three weeks of observation had been secured, or something more than a mere amateur idea of what the telescope was capable of doing; and as he gave up the Observatory to me for the time entirely, and as I worked these alone, I can answer, and indeed am answerable, for whatever was done in it during that period, especially for any errors or shortcomings of my own. A.—2. Present Condition. The patrimonial estate of Elchies lies on the banks of the Spey, about 8 miles below the junction of that river and the Avon, in Lat. N. 57° 28', and Long. W. 3° 15' nearly. The house, which is on a considerably elevated plateau, stands, together with the observatory a few yards from its south-eastern corner, on a broad lawn surrounded by well-grown trees. There is an ornamental portico to the observatory, decorated, not at all inappropriately, with Egyptian emblems, carved in native stone, and also a small transit room; but the chief bulk of the whole structure consists of the large circular equatorial room, about 25 feet in diameter, and furnished with a metal-covered conical dome. This dome has attached to it wheels of one foot in diameter; and, for motion, is revolved on them, while they roll on a fixed circular rail attached to the wall; impulse being communicated by means of toothed gearing and a hand-crank, which acts sufficiently easily. The shutters of the dome, four in number and arranged in two pairs, an upper and a lower one, open to the sky right and left. This they do by sliding on and off the opening of the dome in a peculiar, and as far as I know, a novel manner, with a sort of parallel motion movement in their own plane; each shutter being carried by two pivots, formed in the ends of two strong iron arms, which again work on their own fixed centres on the dome, and GREAT REFRACTING TELESCOPE AT ELCHIES, IN MORAYSHIRE. 373 have counterpoise weights beyond. These shutters were always most satisfactory and true in their movement, opening and closing with facility, and either offering a very large and broad view of the heavens, or keeping out both wind and wet with perfection. The equatorial mounting is of that character usually known as the German variety in form, though in this instance it is constructed in the stronger manner of English engineering work; and has been so abundantly described already in print—1st, in the Jury reports of the Exhibition of 1851; and, 2d, in the Royal Astronomical Society's Monthly Notices for November 1862—that little more need be said of that part of the subject here. Though indeed it is proper to record, considering the great size and weight of the instrument, that I found the hand- ling and working of it by myself alone, far more easy than I had expected; ex- periencing too, throughout the whole of the observations, a remarkable freedom from tremors either of tube or mounting; a consequence, without doubt, of the superior weight, and very massive construction of all those larger parts, which the optician, Mr Ross, had wisely confided to the hands of the well-known manu- facturing firm of RANSOMES and MAY, at Ipswich, to execute for him. A.—3. Preparations for Observing. These preparations consisted in little more than cleaning the instrument from old and hardened oil, cleaning both outer and inner sides of object-glass, but with- out separating the lenses; removing paint from, and brightly polishing, the outer surface of the metal dew-cap; reddening the lamp illumination of the field of view, determining the magnifying power of the eyepiece employed throughout (and found to be 397),* testing the equatorial adjustments and micrometer values, chiefly by daylight observations on known stars, and then in preparing the list of objects to be examined. These were, for the most part, selected from the double and compound stars which I had begun to observe on the Peak of Tene- riffe in 1856, but had had no opportunity of reobserving since then. It was part of the preparation also to endeavour to form some idea of the quality of the object-glass about to be employed ; an object-glass which, though furnished by Mr Ross, is said to have been actually constructed in the optical factories of Munich. There are many small bubbles in the material, but no percep- tible striae; and the discs which are given to the stars when in focus are extremely small,—so small that the two stars B and C of 7 Andromedse, stars of the fifth and sixth magnitudes respectively, and 0-6 of a second apart, were on one occa- * This high power could be kept constantly on, without inconvenience when first picking up any small star, owing to the luxurious furnishing of finders to the large telescope, for it had no less than three such appendages ; whereof the first had a 4-5-inch object-glass, and a magnifying power of 56 times ; the second, a 2-2-inch object-glass, and magnifying power of 28 times; and the third, a 1'7-inch object-glass, and magnifying power of 17 times. 374 PROFESSOE C. PIAZZI SMYTH ON THE sion seen completely separated, well-formed, and with dark sky between them ; a decided advance on what I have ever witnessed with 7 and 9-inch object-glasses elsewhere by celebrated makers. The larger luminous discs also, which the Elchies object-glass gives to stars, on being thrown much out of focus,—and a Lyrse was the one principally experi- mented on,—were pretty regular in their circular formation and strength of illu- mination, though they had a disagreeable feature of colour ; for when the eye- piece was pulled outwards from the focus, the disc was greenish, with a violet border or fringe; but when pushed inwards therefrom, there appeared a small central disc of violet, with an annular surrounding space of green; and when set exactly to the focus, the central part of the star was white, or slightly yellowish, astonishingly brilliant, and surrounded with rays that showed an intense violet colour towards their outer ends.