m, ETC. 8. W. BurnhaM* Astron. (Yerkw) R E P o R T OF MR. TEBBUTT'S OBSERVATORY, WINDSOR, NEW SOUTH WALES, FOR THK YEAR 1888, JOHN TEBBUTT, Fellow of the Royal Astronomical Society, London; Member of the Royal Society of New South Wales, and Corresponding Member of the Ethnographic - Institute, Paris, and of the Queensland Branch of the Royal Geographical Society of Australasia. !Syrltic^i : GEORGE MURE AY & CO., PRINTERS, 91 CLAKE3SCE STREET. 1889. REPORT OF MR. TEBBUTT'S OBSERVATORY, WINDSOR, NEW SOUTH WALES, FOR THE VICAR 1888, \ 13 Y JOHN TEBBUTT, Fellow of the Royal Astronomical Society, London; Member of the Royal Society of 2\eiv South JFales, and Corresponding Member of the Ethnographic Institute, Paris, and of the Queensland Branch of the Royal Geographical Society of Australasia. JSytlncy : GEORGE MURRAY & CO., PRINTERS, 91 CLARENCE STREET. 1880. CONTENTS. ♦ PAGE. Buildings and Instruments 5 Geographical Position of the Observatory 6 Meridian Work 7 Instrumental Errors and Chronometer Errors and Hates 11 Extra-Meridian Work 19 Meteorological Observations 22 Publications "• 22 The Library 25 Personal Establishment 26 Proposed Work for year 1889 26 Observations Utilised since 1887 27 Conclusion 27 Presents received for the Library from September 1st, 1887, to December 31st, 1888 28 REPORT OF THE WINDSOR OBSERVATORY. For 1Q88. ♦ At the close of the year 1887, a pamphlet of 74 pages was published, entitled a "History and Description of Mr. Tebbutt's Observatory, Windsor, New South "Wales." This little volume contains a detailed account of the Observatory buildings and of their instrumental equip¬ ment, and furnishes a list of all the scientific papers published by the proprietor, and of presents to the Observatory library, down to the close of August, 1887. The present Report will bring down the History of the Observatory to the close of the year 1888, under various heads, as follow :— Buildings and Instruments. These remain as they were at the close of August, 1887, so that a description of them will be unnecessary here. A general notion of the buildings can be formed from the frontispiece of the publication referred to. It will suffice to state that the principal instruments are a 3-inch transit instrument, by Cooke and Sons of York ; a sidereal and a mean-time chronometer, by Parkinson and Prodsham and by Poole, respectively; an 8-inch equatorial, by Grubb of Dublin; a 4^-inch equatorial, by Cooke and Sons; and a SJ-inch refractor, by Jones. [ 6 ] Geographical Position of the Observatory. The best local determination of the longitude is that published by the author in R. Ast. Society's Monthly Notices, Yol. XL., p. 440. The result is lOh. 3m. 21.81s. E. of Greenwich, and is derived from twenty-three occultation phases, namely, nineteen disappearances and four reappearances. The occulted stars are well known ones, and the moon's tabular places were corrected from meridian observations at Greenwich, Radcliffe, and Washington. With a view to obtain a fundamental meridian for the Australian Colonies from absolute methods, Dr. Auwers of Berlin, in 1884, discussed a series of seventy-six disappearances of stars at the moon's dark limb, observed at Windsor in the years 1873, 1874, 1875, and 1876, and arrived at lOh. 3m. 21.25s. E. as the longitude of Windsor, a result which differs only 0.56s. from that just mentioned. Combining this value with that derived for Melbourne from ten disappearances and two reappearances in the years 1874 and 1875, with moon-culmination results at Sydney and Melbourne, and approximate values of the telegraphic differences of longitude between Sydney and Melbourne and Sydney and Windsor, he derived lOh. 4m. 49.60s. E. as the longitude of Sydney. Subtracting 1m. 28.83s. from this result, he gets lOh. 3m. 20.77s. E. as the longitude of Windsor. In 1887, Professor Harkness of Washington, recognising the great importance of the result derived for Windsor from the occultations of 1873-76, suggested to me the desirability of determining with all possible accuracy the differences of longitude between the Windsor Observatory and the Government Observatories at Sydney and Melbourne. Immediately on the receipt of Professor Harkness' letter, I communi¬ cated with Mr. Lenehan, the Acting Government Astronomer at Sydney, and Mr. Ellery, the Government Astronomer at Melbourne, and the result was that exchanges of telegraphic signals were made with the most satisfactory results, as described in a paper read before the Royal Astronomical Society in April, 1888, and published in the Society's Notices, Yol. XLVIIL, p. 313. The Windsor observations, in full detail, were [ 7 ] forwarded to Professor Harkness, together Avitk the Sydney and Melbourne signals, clock-errors, and rates. He proposes to work out the Windsor chronometer errors and rates by the method of least squares, in order to get the best possible values from the observations. Mean¬ while, adopting 1m. 29.39s. and 24m. 55.26s. as the differences of longitude between Sydney and "Windsor and Sydney and Melbourne respectively (see the author's paper above referred to), and applying these amended differences according to the combination employed by Dr. Auwers, we get lOh. 4m. 49.90s. E. and lOh. 3m. 20.51s. E. as the longitudes of Sydney and Windsor from Greenwich. Considering the number of links in the whole chain of telegraphic connection with Greenwich, this result is probably as trustworthy as that derived from the late telegraphic connection with Singapore. The most reliable value of the latitude is — 33° 36 30.8 , which was derived from a series of prime vertical observations, in 1881, of well- determined stars close to the zenith with the 3-inch transit instrument. (See the author's paper in R.A.S. Monthly Notices, Yol. XLIY., p. 101.) Nothing further has been done in the way of investigating the latitude, if we except the circumstance that in 1887 the" author made a trigonometrical connection between the Obser¬ vatory transit-instrument and the north terminal of the Government base-line, about three miles nearly due west of the Observatory. This connection, which was estab¬ lished with an ordinary steel tape and a 5-inch theodolite reading to minutes of arc, gave - 33° 36' 30.5" as the latitude of the transit and equatorial piers, which differs only 0.3" from the value obtained directly from the prime vertical observations of 1881. The geographical latitude of the terminal as furnished by the head of the Trigonometrical Survey is —33° 35' 58.07". Meridian Work. This has been done throughout with the 3-inch transit instrument in connection with sidereal chrono¬ meter (Parkinson and Erodsham) No. 1042. The transit system consists of five wires, designated A, B, C, D, and [ 8 ] E, in the order of transit above the pole when the clamp is east. The equatorial distances in sidereal time of the four outer wires from the middle wire were re-determined from all the transits of circumpolar stars observed in 1887, with the following results:—Ah- 19.492s. B+9.782s. D—10.001s. E —19.656s., which have been employed throughout the reductions of 1888. The reduction for a complete observation of an equatorial star at the upper culmination, clamp east, has therefore been—0.077s. The reduction for any other star is this quantity multi¬ plied by the secant of the star's declination, and has been taken from a MS. table having for its argument the star's declination. For incomplete transits the reduction for an equatorial star is taken from a MS. table giving the algebraic means of the observed wires. The observations have all been made by the eye and ear method. The level and azimuth errors of the transit instrument, considering the founda¬ tion of the pier, which consists of clay and loam, have been pretty steady throughout the year. The level employed is a striding one of 1130 feet radius, each division being equal to 0.8". The inclination was determined once at least on each evening of observation by four readings of each extremity of the bubble, the level being twice reversed during the operation. On some occasions, and always when the transit instrument has been reversed, two or more sets of readings have been taken. When the western pivot is the higher, the level error is regarded as positive. The collimation error was determined at intervals of a few days by comparing the middle wire in both positions of the axis of rotation with the corresponding wire of a two-inch transit instru¬ ment on a pier a little north of the transit-room. The middle wire of the collimator is slightly inclined for the purpose, and the comparison is always made near the horizontal wires. As there is no micrometer in connec¬ tion with the transit system, the distance of the middle wire from that of the collimator is estimated for each position of the axis of rotation in terms of the diameter of the wire. Half the total displacement reduced to seconds of arc from the known diameter of the wire is [ 9 ] regarded as the collimation error. "When the middle wire falls east of the collimation axis of the telescope with the clamp east, the collimation error is regarded as positive. On every occasion when the instrument has been reversed, star transits have been observed in both positions of the rotation axis, and by allowing for chronometer rate, it has been found that the estimations for collimation error are quite as reliable as the results which might be obtained by the application of the micro¬ meter to so small an instrument. The collimation errors for dates between those on which the reversals were made are simply interpolated.