(B.) The Longitude of the Colonial Observatory, Wellington.
The subject of New Zealand standard time naturally leads to the cognate subject of the longitude of the standard meridian of the time-service, or, in other words, of the longitude of the Wellington Observatory. This already has a voluminous literature of its own; but the details are scattered over so many parliamentary reports and past volumes of the “Transactions of the New Zealand Institute” that it will be useful for purposes of future reference if the essential facts are brought together in one paper.
Before dealing with the question of the longitude, perhaps I may be allowed to give a few particulars about the Observatory and its origin. The present Wellington Observatory was established in 1869 as a result of the decision of Parliament to institute one uniform time for the colony. It is a time-service observatory pure and simple, and therefore structurally it is of but modest proportions, consisting merely of a transit-room and a clock-room. Its equipment, however, is of the best, and entirely sufficient for the purpose. The transit instrument, of 2 ¾ in aperture and 32 in. focal length, is an excellent one by Troughton and Simms. It is substantially mounted in the usual way on a pyramidal brick pier resting on a solid foundation of rock, and is duly isolated from contact with the building and carefully protected from surface tremor. The meridian-mark is a 3 in. iron pillar, deeply set in concrete, standing about 6 ft. high on the sky-line of the Tinakori Range, a sufficient distance to the northward, near Wadestown. There are four fine clocks—one of them a sidereal clock, and the other three mean solar time clocks. They are mounted on brick and cement bases, and are fastened to substantial timber frames stayed by steel rods to prevent disturbance of the adjustments. They are good time-keepers; and, as there are three mean time clocks, by a combination of the rates practically true time can always be given, even when bad weather stands in the way of observations. The sidereal clock, by Dent, is provided with a magnetic chronograph by the same
maker. One of the mean time clocks is also by Dent, and is an instrument of the same class as the sidereal clock, with zinc and steel compensation. A second mean time clock, by Moore, of Clerkenwell, has a mercurial compensation; and the third mean time clock, by Moore, is the one which drops the time-ball and sends signals to various parts of the colony. This clock is fitted with an electro-magnetic apparatus which enables the clock to signal time automatically every hour to certain places in town (the Museum, the Telegraph Office, and the shops of the leading watch-makers) and to drop the time-ball on Waterloo Quay at noon each day. The same clock is frequently placed in direct connection with the telegraph offices at Lyttelton and Port Chalmers, and thus signals true time, without human intervention, for the use of navigators at those ports. If the time-balls at Lyttelton and Port Chalmers—and, indeed, the one at Auckland also—were equipped with the necessary electro-magnetic dropping gear, they could be operated by the clock direct from the Observatory, just as our own time-ball now is; a distinctly better plan than the present one, under which uniformity of time at the several ports is not easily secured. Still, any navigator at Auckland, Lyttelton, or Dunedin (or at any other port) can, through the co-operation of the Telegraph Department, obtain time-signals direct from Wellington Observatory in case he feels dissatisfied with the indications given him by the local time-balls; and this opportunity is frequently taken advantage of by the commanders of merchant ships and the navigating officers of men-of-war. Sometimes special signals are sent for important purposes. Thus, when H.M.S. “Penguin” a year ago wished to determine the longitudes of Tauranga and Gisborne, a series of time-signals was exchanged between the Observatory and the ship at each of those two ports; and again, when the antarctic exploring ships “Discovery” and “Morning” were in the colony and about to sail south, a succession of exact signals was sent night after night by special wire from the Observatory to the officers' cabin of either vessel as she lay at the wharf at Lyttelton.
From the magnetic signal which is sent by the clock at 9 a.m. each day to the operating-room of the Wellington Telegraph Office time is repeated by an officer of the Department (using an ordinary Morse instrument) to all the telegraph offices in the colony. This hand-sent signal is not intended for chronometer-rating purposes, and is therefore despatched merely with sufficient accuracy for ordinary office use and for the purpose of enabling all the telegraph and railway clocks in the colony to be set daily to a common time. Practically
every telegraph office and railway-station throughout the country is thus regulated frequently and uniformly to the central time.
The reasons for the selection of Wellington as the position for the Observatory were strong ones. They were set forth by Dr. Hector and the late Archdeacon Stock in 1868, and were emphasized by Chief Surveyors J. T. Thomson and Henry Jackson some three years later. On the 19th October, 1868, the Rev. Mr. Stock, who for about five years previously had been in charge of a small time-ball observatory built by the Provincial Government of Wellington on land now occupied by the General Post Office, addressed a letter to the Hon. John Hall, Postmaster-General, pointing out that the site of the Observatory was no longer suitable, and urging that the General Government should erect an improved Observatory on a more satisfactory spot. In support of this suggestion he wrote: “I need hardly say that Wellington, being the centre of the telegraph system, is the best place for the Observatory, which would have to use the telegraph wires.”*
In a memorandum to the Hon. W. Gisborne, written on the 18th of the following month, Dr. Hector endorsed the suggestion of Mr. Stock and the reasons advanced in its favour, and he proposed the site which was ultimately chosen, a knoll behind the cemetery in Bolton Street.†
Again, on the 21st September, 1871—the Observatory in the meantime having been built and been doing good work—Messrs. Thomson and Jackson, in a report to the Government‡ on the subject of the longitude of the new Observatory in its relation to the longitudes of certain other places in the colony, said, “There will be three points in New Zealand, extending nearly along the whole length, two of which will have been referred to an initial meridian at Wellington. Such being the case, and actuated by the same motives which first induced us to determine the absolute longitudes in our respective provinces, we beg to submit for the consideration of the Government that there shall be an initial meridian for the reference of all longitudes in New Zealand, at Wellington, which, as its capital, and from its central position, is the most eligible site that could be chosen; and that this initial meridian be that of the Government Observatory.”
[Footnote] * Appendix to Journals of House of Representatives, D.-No. 39, 1870.
[Footnote] ‡ Appendix to Journals of House of Representatives, G.-No. 23, 1871.
Ministers gave favourable attention to the proposals submitted to them, the Hon. John Hall minuting Dr. Hector's memorandum with the remark: “As the General Assembly has directed New Zealand mean time to be kept throughout the colony, some provision for ascertaining that time with exactitude is indispensable. The arrangement here suggested seems as good as can be made” (28th November, 1868).*
The erection of the Observatory was accordingly authorised; the building was put in hand at once, and finished in June, 1868; and the instruments were placed in position by the following October. The adjusting of the transit instrument and other necessary arrangements delayed matters until the end of the year; but in January, 1870, the work of the time-service was begun under Dr. Hector as Director and the Rev. Mr. Stock as Observer; and it has been carried on continuously ever since. Archdeacon Stock was Observer until August, 1887, when failing health obliged him to retire.
Early attention was devoted to the longitude of the Observatory. There have been several determinations of this. The most reliable have been effected by means of the fixing of the meridian distance from Sydney Observatory, and the work of determining this difference has been accomplished with close accuracy. But Sydney Observatory, although its longitude, like that of Melbourne Observatory, is now supposed, as the result of direct telegraphic comparison with Green-wich, to be very exactly known, has been yet compelled on several past occasions to revise its assumed longitude. Wellington Observatory, dependent as it has been on Sydney as the prime meridian, has therefore had to make corresponding corrections in its assumed longitude. But these changes have not been serious. Fortunately, Melbourne, at a very much earlier date than Sydney, was able to obtain a longitude which has not called for appreciable revision; and as it was known about thirty years ago that the Melbourne determination was more reliable than the Sydney one (seeing that the Melbourne value had been arrived at by cable from Greenwich, whilst the Sydney value had been obtained from observation), and as, moreover, the difference between the longitudes of Sydney and Melbourne had been ascertained then by the use of the telegraph line, it was possible to arrive at a value for Wellington Observatory derived from the Sydney longitude corrected on the basis of the Melbourne longitude, and this corrected value has been shown by subsequent investigations to have been extremely near the mark.
[Footnote] * Appendix to Journals of House of Representatives, D.-No. 39, 1870.
It is interesting to note some of the alterations which have been made in the recorded longitude of Sydney Observatory during the past thirty years, and to compare them with the smaller corrections which have been necessary in the assumed longitude of Melbourne. From old volumes of the “Nautical Almanac”* and from other sources we find that since 1874 the following values have been used for these two observatories:—
The first reliable determination of the difference of longitude between Sydney and Wellington was effected in the years 1852 and 1854 by H.M. ships “Acheron” and “Pandora,” under Captain J. L. Stokes and Commanders G. H. Richards and B. Drury, by the transport of chronometers from Sydney to Wellington during the course of the complete survey made by those vessels of the New Zealand coast. The place selected in Wellington was a spot near Pipitea Point, on what is now the railway-line (it used to be marked on the old charts as “Observation Spot”). When the Observatory was afterwards built its difference of longitude from that position (viz., 2.88 s.§) was easily ascertained by triangulation. The result thus obtained was subsequently confirmed by telegraphic determinations. In 1876 Mr. H. C. Russell at Sydney Observatory and Archdeacon Stock at Wellington Observatory exchanged a series of cable time-signals which gave a mean result accordant with that of Captain Stokes to within about half a second of time, showing how admirably that officer had done his work;‖ and again, in 1883, Mr. Russell at Sydney Observatory and
[Footnote] * See “Nautical Almanac” for 1883, 1889, 1894, 1896, 1897, 1898, and 1903.
[Footnote] † Absolute determination.
[Footnote] ‡ Present Value.
[Footnote] § The transit pier of the Observatory is 5015.6 links west of Observation Spot at Pipitea, equal to 2.88 s. in time.
[Footnote] ‖ See Trans. N.Z. Inst., vol. ix., 1876, p. 217: “On the Longitude of Wellington Observatory,” by Ven. Archdeacon Stock, B.A.
Mr. O. W. Adams, New Zealand Geodesical Surveyor, at the Survey Department's observatory which then stood on the site at Mount Cook afterwards taken for the prison buildings, by another series of careful telegraphic exchanges arrived at a result almost identical with that of Mr. Russell and Archdeacon Stock, allowance, of course, being made for the difference (1.21 s.*) between the longitudes of Mount Cook Observatory and Wellington Observatory, as derived from triangulation. (The respective personal equations of Mr. Russell and Mr. Adams were tested and taken into account in the final examination of their work.) These three determinations compare as follows:—
|Wellington Observatory East of Sydney Observatory.|
|Stokes's chronometric determination||1||34||15.28|
|Russell and Stock's telegraphic determination||1||34||15.99|
|Russell and Adams's "||1||34||15.77|
There was another chronometric determination—viz., by Captain G. S. Nares, of H.M.S. “Challenger” (see his memorandum to Dr. Hector, printed in vol. vii. of the “Transactions of the New Zealand Institute,” 1874, p. 502). This gave the meridian distance of Wellington Observatory as 1 h. 34 m. 17.23 s. E. of Sydney Observatory; but, as Captain Nares himself pointed out, his result was not so trustworthy as that of Captain Stokes, as an interval of twenty-one days elapsed between the “Challenger's” observations at Sydney and Wellington, whereas Captain Stokes is supposed to have run his distance directly from Sydney to Wellington, and thus to have secured his observations at the two ports within a less interval of time. Captain Nares's determination was therefore not accepted.
The following table shows the several longitudes for Wellington Observatory resulting from these determinations, with the changes rendered necessary from time to time by the corrections made in the longitude of Sydney:—
[Footnote] * Mount Cook Observatory was east of Wellington Observatory 2097.2 links = 1.21 s., as is shown in a copy of a departmental memorandum kindly furnished to me by Mr. Marchant, Surveyor-General.
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Determination.||Longitude of Sydney Observatory being assumed as||Difference of Longitude, Wellington-Sydney Observatories||Resulting Longitude for Wellington Observatory.||Remarks.|
|H. M. S.||H. M. S.||H. M. S.|
|Stokes's chronometric||10 4 53.37 (absolute determination)||1 34 15.28||11 39 8.65||This was the value placed on the charts (i.e., Pipitea Point= 11 h.39 m. 11.53 s. deducting from which 2.88s.—the difference between Pipitea Point and the Observatory—We get 11h.39m. 8.65s.).*|
|Ditto||10 4 53.90||1 34 15.28||11 39 9.18||As in Archdeacon Stock's paper “On the Longitude of Wellington Observatory,” 1876, Trans. N.Z: Inst., vol. ix., p.217.|
|Ditto||10 4 50.61 (depending on Melbourne)||1 34 15.28||11 39 5.89||As in Dr. Hector's letter of 9th September, 1874, to Colonial Secretary, covering memorandum from Captain G.S. Nares, of H.M.S. “Challenger” (Trans. N.Z.Inst., 1874, vol. vii., p.502), also as in Major H.S. Palmer's Report on Longitudes, 1875-76, in Appendix to Journals of House of Representatives, H.-No. 6, 1876.|
|Ditto||10 4 49.54 (telegraphic determination now accepted)||1 34 15.28||11 39 4.82|
|Russell and Stock's telegraphic (1876)||10 4 50.61 (depending on Melbourne)||1 34 15.99||11 39 6.60||See Archdeacon Stock's paper above mentioned.|
|Ditto||10 4 49.54 (accepted telegraphic)||1 34 15.99||11 39 5.53|
|Russell and Adams's telegraphic (1883)||10 4 48.47||1 34 15.77||11 39 4.24||Sydney Observatory to Mount Cook Observatory, 1h. 34m. 16.98s., less difference Mount Cook and Wellington Observatories 1.21s. = 1h.34m. 15.77s.|
|Ditto||10 4 49.54 (accepted telegraphic)||1 34 15.77||11 39 5.31|
[Footnote] * See Report of Board of Longitude, Appendix to Journals of House of Representatives, D.-No.27, 1870.
In addition to these chronometric and telegraphic determinations, there have been three “absolute” determinations—that is, determinations by means of observations of moon culminations, &c. Before the present Observatory was built, Captain Carkeek, with the view of ascertaining the longitude of the old time-ball tower, conducted for many years a series of observations in the shape of lunars, eclipses of Jupiter's satellites, lunar eclipses, and moon culminations.
Then, in 1869, 1870, and 1871, Chief Surveyors J. T. Thomson and Henry Jackson, at their respective private observatories at Rockyside (Caversham, Dunedin) and the Hutt, by observations of moon culminations determined the longitudes of those points. Having done so, they settled by means of the electric telegraph the difference between the longitudes of their two observatories, as a check upon their independent determinations. Mr. James McKerrow, afterwards Surveyor-General, assisted Mr. Thomson at Rockyside in this important branch of the work.
By triangulation from the old time-ball site to the Wellington Observatory, and from Mr. Henry Jackson's private observatory to Wellington Observatory, values were thus obtained for the longitude of Wellington Observatory.
Finally, in 1874-75, Major H. S. Palmer, R.E., chief of the English expedition to New Zealand for the observation of the 1874 transit of Venus, conducted a series of observations at Burnham (his observing-station in Canterbury) for the determination of the longitude of that place. Professor C. H. F. Peters, chief of the United States Transit of Venus party, about the same time made similar observations for longitude at his station at Queenstown, Lake Wakatipu. Then these two points, with Mr. Heale's temporary observatory at Auckland, the Colonial Observatory at Wellington, and Mr. Thomson's observatory at Caversham, were connected by telegraph, with the object of ascertaining their respective differences of longitude. Major Palmer himself came to Wellington and conducted the work necessary for fixing the longitude of the Wellington Observatory on this basis.
The results of these absolute determinations (or, to use Major Palmer's term, “approximate absolute determinations”) were as follows:—
(1.) Captain Carkeek's approximate absolute,* 11 h. 39 m. 15-75 s. E.
(2.) Messrs. Thomson and Jackson's approximate absolute,* 11 h. 39m. 15-31 s. E.
[Footnote] * For an account of Captain Carkeek's and Messrs. Thomson and Jackson's determinations see Messrs. Thomson and Jackson's report to Government, Appendix to Journals of House of Representatives, G.-No.-23, 1871.
(3.) Major Palmer's approximate absolute,* 11 h. 39 m. 4–81 s. E.
Major Palmer's result, it will be seen, is identical to within a hundredth of a second of time with the value which has been obtained from Captain Stokes's chronometric work when the most recently accepted longitude for Sydney Observatory is used. On the other hand, the results deduced from Captain Carkeek's and Messrs. Thomson and Jackson's observations seem at first sight a good deal out of line with all the other determinations. They were consequently not taken into account in deciding upon the longitude to be used for the purposes of the time-service. But Major Palmer showed in his report some four years later that Messrs. Thomson and Jackson's determination was susceptible of treatment which placed it in a different light. Messrs. Thomson and Jackson, in reducing their observations, had not taken into account the errors of the moon's tabular place. Major Palmer pointed out that the average of these errors for the days on which the moon was observed at Rockyside and the Hutt was about 0–25 s., which would probably cause an error of between + 6 s. and + 7 s. in the resulting longitude;† therefore Messrs. Thomson and Jackson's corrected longitude of the Observatory might be taken approximately as 11 h. 39 m. 9 s. E. This differs from the ultimately accepted longitude by less than 4 s., very little more than the error (3-29 s.) which shortly before this had had to be recognised in the absolutely determined longitude of Sydney Observatory. The problem of exactly ascertaining a longitude by observation is notoriously one of extreme practical difficulty; and Messrs. Thomson and Jackson's result, when subjected to this revision by Major Palmer, showed that their long and patient series of observations had been carried out with much skill and care, and was an honourable and worthy piece of work. The details of Captain Carkeek's calculations are not available, as they were accidentally destroyed many years ago by fire.
To sum up, it will be seen that all the foregoing determinations may be arranged in two groups—one with a value of about 11 h. 39 m. 9 s., and the other with a value of about 11 h. 39 m. 5 s. The former of these approximate values was practically known as long ago as 1874 to be erroneous; the latter by the same year was believed to be correct, and two years later was known to be correct, on the assumption that Sydney's longitude was reliable. Sydney's 1903 value differs by only about 1 s. from its 1874 value; so that Dr. Hector
[Footnote] * For details of Major Palmer's work see his report to Government, Appendix to Journals of House of Representatives, H. No. 6, 1876.
[Footnote] † See Loomis's “Practical Astromony,” p. 316 (seventh edition).
was a true prophet when in 1874 he expressed the belief that the “probable true longitude of Wellington Observatory” was 11 h. 39 m. 5–89 s.* Of course, it would be rash to say that no future revision may be necessary; but we seem warranted in thinking that any correction which may be called for will be but trifling.
But although the longitude was thus corrected so many years ago, the old value of 11 h. 39 m. 9 s. has up to the present time continued to be used by the Admiralty as the basis of its charts of New Zealand; consequently all positions in the colony as shown on these charts (with the exception of one sheet to be presently mentioned) are out in longitude to the extent of between 3 ½ s. and 4 s. of time, or something under a mile. In view of the smallness of this error (which would not be a source of any danger to navigators), the Admiralty has no present intention of altering its charts. There are fifteen sectional charts of the coasts of the colony, besides many sheets of individual ports and of special anchorages; and to amend the longitudes on all of these would entail much expense in erasing lines on the plates and in regraduating the charts. Seeing, then, that this old longitude has been retained on the charts, it has also heretofore been retained as the working longitude of the Observatory in computing time for general and navigation purposes,† as it has been judged highly convenient to have the time-service basis identical with the chart basis so long as there seemed any chance that the amended value of the longitude might be open to further revision.
A Board of Longitude was appointed by the New Zealand Government on the 8th July, 1869, to report upon the longitude of Wellington and of other parts of the colony in relation to the initial meridian of Wellington. The Board consisted of Dr. Hector (Chairman), the Rev. A. Stock, Mr. Henry Jackson, Chief Surveyor of the Province of Wellington, and Mr. G. A. Woods, Colonial Marine Surveyor. After going into the question thoroughly, and conferring with Mr. Ellery, Government Astronomer of Victoria, the Board reported‡ in favour of adopting provisionally the chart longitude, instead of keeping the question open longer for the sake of any small error which might ultimately be ascertained. A similar view was expressed by Major Palmer in his 1875 report; and that gentleman suggested
[Footnote] * Trans. N.Z. Inst., vol. vii., p. 504.
[Footnote] † But of course the amended longitude has been used for scientific purposes which have called for nice accuracy—such as the observations of the transits of Venus in 1874 and 1882.
[Footnote] ‡ Appendix to Journals of House of Representatives, D.–No. 27, 1870.
that no change should be made until by means of the then projected submarine cable a telegraphic longitude-difference should have been obtained between New Zealand and Sydney or Melbourne.
The frequent corrections which have been found necessary in Sydney's assumed longitude since then have caused the change to be postponed longer than was originally contemplated. But circumstances now seem favourable for making it. The last alterations in the longitudes of Sydney and Melbourne were announced in the “Nautical Almanac” for 1898 (published in November, 1894); and as these were based on very careful telegraphic determinations by observers at Greenwich, Sydney, and Melbourne, they seem likely to be practically final. Moreover, the Admiralty has in one case used the latest longitude in compiling a chart.
On the sheet to which I have referred as forming an exception to the others—viz., the large-scale chart of Port Nicholson (No. 1423)—the longitude is given as 174° 46′ 20″, equivalent to 11 h. 39 m. 5*3 s. The Hydrographer to the Admiralty, in a letter written by him to Sir James Hector on the 1st December, 1902, explains that this determination (which was the one given in the report of the Australian Telegraphic Determination of Longitudes, 1886) was adopted by the Admiralty in 1890, and that, although it has not been considered necessary in the interests of navigation to alter the existing coast, charts, the value 11 h. 39 m. 5.3 s. will be the initial point of any rearrangement which may ultimately be made in the Admiralty charts. He agrees that, under the circumstances (the discrepancy being so small), the determination of the Admiralty to retain the old longitude on the majority of the charts need be no further bar to our “adopting the quantity which is at present considered to be the most correct.” The value given on the large-scale chart (No. 1423) is that obtained from Mr. Russell's and Mr. Adams's telegraphic work in 1883; and as this differs by only 0.2 s. from the value deduced from Mr. Russell's and Archdeacon Stock's telegraphic interchange in 1876 the way is now clear for using 11 h. 39 m. 5*3 s. as the standard longitude for computing. New Zealand mean time from observations taken at the Observatory.
A similar small error occurs in the longitudes given in the Survey Department's land maps of the colony. These longitudes are based on Mr. Thomson's determination of the longitude of Rockyside (as amended in the manner above explained); consequently the values are at present practically identical with those shown in the charts. I understand, however, that the Surveyor-General purposes taking advantage of an intended reissue of the Department's maps to
[Footnote] * Viz., 11 h. 39 m. 6–52s. for Mount Cook Observatory, which was 1–21 s. east of Wellington Observatory.