I would like to acknowledge Dr Wayne Orchiston, with whom this was originally planned to be a joint paper. Thanks are due to helpful comments from the editors of this special issue, from the journal editors and from two anonymous referees.
1In the second half of the 19th century the two main astronomical observatories in Australia were the Sydney and Melbourne observatories. Their directors for most of the period, Henry Chamberlain Russell (1836-1907) at Sydney and Robert L.J. Ellery (1827-1908) at Melbourne, were dominant figures in the science of the country. Both observatories had their precursors: Parramatta for Sydney and Williamstown for Melbourne. Like other observatories of the era, all four were involved in the measuring of star positions, in the determination of longitude and latitude and keeping time. Hence, all of them had transit circles. For its first two decades, Sydney Observatory used the transit circle it inherited from Parramatta, while Melbourne Observatory initially also used the one from Williamstown.
2This paper collects for the first time all available information, some of it archival, on the four transit circles used at Sydney and Melbourne observatories. We look at the makers of the instruments, how they were ordered, where, how and by whom they were used and the difficulties caused by the distance from the makers and the main centres of astronomical research in Europe. Most importantly, we consider if useful observations could be made with the instruments despite the challenges involved. One way each of the local astronomers in charge of the transit circles tried to achieve worthwhile results was to modify their instrument to fit in with their conditions and habits to form an assemblage of observer and telescope.
3Parramatta Observatory, established in 1822, was the second major observatory in the Colony of New South Wales. Initially, it did not have a transit circle and star positions were obtained with a combination of a transit telescope and a mural circle. Obtaining star position with the two separate devices of a transit telescope and a mural circle was difficult, especially for a single observer. Combining the two instruments into one in the form of a meridian or transit circle greatly increased the efficiency of observing.
4One of the first such instruments was the one made by Edward Troughton (1753-1835) in 1806 for the English amateur astronomer Stephen Groombridge (1775-1832) (Schaffer, 2010, p. 131). When Carl Rümker, who was in then charge at Parramatta, arrived in England to purchase a transit circle, the Groombridge circle belonged to the astronomer James South (1785-1867), who offered to sell it to him for £400 (Saunders, 1990, p. 251-252). However, when the sale was imminent South increased the price to £650. Rümker, claiming to save the British Government from being defrauded, then ordered the circle instead from Thomas Jones (1775-1852) of Charing Cross, London for £400.
5The transit circle arrived at Parramatta in 1835 and James Dunlop, Rümker’s replacement in charge of the Observatory, mounted it and began using it on 28 April (Russell, 1888, p. 68), soon after its arrival. His first project was to observe the same stars with the new circle and with the mural circle to find the errors in the latter instrument.
6The best description of the transit circle is from the report of commission of enquiry into Parramatta Observatory in 1847 (Russell, 1888, p. 80-82) and it is brief: “A Meridian Circle, forty-two inches [1.07-m] diameter, by Jones, the Telescope having an aperture of three and three-quarters inches [9.5 cm].” An idea of the instrument can be formed from the cross-sectional drawing (Figure 1), published in the Sydney Observatory report for 1859 (Scott, 1860, p. ii), that shows the telescope asymmetrically placed on its conical axis. Another indication can be found from the larger Radcliffe Circle that Jones produced at the same time as the one for Parramatta. This instrument, now in the collection of the History of Science Museum, Oxford, was of six feet (1.83-m) diameter and its telescope had a lens with a 4.1 inches (10.4 cm) aperture.1 It appears a close match to the diagram of the Parramatta instrument. The former display label for the Radcliffe Circle quotes Jones as describing it as a “Mural Transit Circle” and states that it represents an intermediate stage in the evolution from a mural circle to a meridian circle.
7On setting up the new transit circle, Dunlop quickly found problems with it. The spirit level, used to keep the instrument’s axis horizontal, was filled with diethyl ether, a liquid with a low boiling point of 34.6° C, and it burst after a few months in the Australian sunshine (Russell, 1888, p. 80-86).
Figure 1 - Cross-sectional drawing of the Parramatta Transit Circle
Source: William Scott (1860), Astronomical Observations Made at the Sydney Observatory in the Year 1859, Sydney, Thomas Richards, Government Printer, page ii
- 2 This was a design fault on the instrument. Errors due to eccentricity can only be detected and eli (...)
8There were only three microscopes on the instrument, instead of the usual four, and that meant, as Dunlop pointed out, that errors due to eccentricity — the off-centre condition of the circle — could not be detected.2 Dunlop said in his 1847 letter of resignation, quoted by Russell, “Altogether it is an unhandy instrument”, while the report of the commission of enquiry quotes him as stating that it is “so very unsatisfactory in its fittings and the graduation of the Circle itself as to be quite useless” (Russell, 1888, p. 82).
- 3 The first two catalogues listed are whole sky catalogues, with the second including stars selected (...)
- 4 North polar distances are equal to 90°- declination. They were used instead of declination for bot (...)
- 5 Sydney Observatory unpublished report for 1866, Sydney Observatory archives. To form the marker tw (...)
9Due to its problems, the transit circle was sent back to England for repairs prior to use at the new Sydney Observatory (Scott, 1859). It arrived late in 1858, the first year of the observatory’s operation but setting it up took some time (Scott, 1861). William Scott (1825-1917), the first Government Astronomer at the observatory, began regular observations with the instrument in June of the following year. He selected stars given in the Nautical Almanac, the British Association Catalogue (Baily, 1845) and Lacaille’s New Catalogue (Baily, 1847)3 and within 10° of the zenith*. For the selected stars he made transit and zenith distance observations that were converted to right ascensions* and north polar distances4 for the epoch 1 January 1859. Scott estimated the errors from the internal consistency of these values. There were some temporary errors, such as those from the shrinking of the sandstone piers, and observational errors that could be minimised by taking averages of four or five observations. The main problems, however, were instrumental, including from irregularity in the pivots. The consequence, according to Scott, was that: “Although the circle may be regarded for some purposes as a useful instrument, yet it cannot be classed among instruments of the highest order, nor can its results compare in accuracy with those obtained at the Royal Observatory at the Cape of Good Hope.” (Scott, 1861) Despite these issues, Scott persevered and published 884 meridian observations of stars for 1859, 2507 for 1860 and 2100 for 1861, together with observations of Moon culminations and comet positions (Russell, 1882). Scott resigned in 1862 and his successor George Robarts Smalley (1822-1870), noting the problems with the transit circle, decided to only use the instrument for time determination. However, during Smalley’s time a solid stone pillar, one of six from the demolished old Sydney General Post Office, was erected on high ground on the other side of Sydney Harbour, at 2.7 km distance from the observatory, to provide a north marker for the telescope.5
10Once there was no further use for the old Parramatta instrument, Sydney Observatory staff sent it to the University of Sydney on 27 October 1905 (Masters and Raymond, 1909). It has not been returned and no trace of it has been found at the university.
11After the death of Smalley in 1870, Henry Chamberlain Russell (1836-1907), who had been the assistant astronomer at the observatory since 1859, was appointed as Government Astronomer (Bhathal, 1991). Russell was also dismissive of the old transit circle from Parramatta and he managed to gain authorization to purchase a new instrument prior to his departure on a trip to England in 1875 (Russell, 1876). After inspecting offerings from several makers of scientific instruments, he gave the order to James Simms (1828-1915) (Turner, 1916) of Troughton and Simms, an instrument making firm located at Charlton, Kent in England. Russell proudly stated that: “The instrument will combine all the most recent improvements and some that are used in it for the first time. I believe it will be one of the finest instruments extant.” (Russell, 1876)
12The Colonial Government allowed Russell to purchase the new transit circle to satisfy the needs of the Trigonometrical Survey of New South Wales (Orchiston, 1987). This survey had been started by Smalley, but Russell when became Government astronomer had managed to transfer the task to the Surveyor-General and his staff (Wood, 1958 p. 13). Russell was authorised to spend £700 but it was insufficient.6 After his return from the England, on 28 October 1875 Russell wrote to the Surveyor-General stating that an extra £240 was needed to cover the cost of the microscopes required for reading the circles on the instrument, as well as an extra £10 for the cost of shipment to Australia.7 He finished the letter with a request: “As this instrument is required for work connected with the Trigonometrical Survey, perhaps the sum required to complete it may be provided from the vote for that purpose”.
- 8 H.C. Russell to J. Simms, 17 November 1876, State Records NSW, Series A 3003, Box 37.
13The request must have been granted as the instrument did arrive and with the necessary microscopes. However, the instrument did not arrive quickly and this put Russell in difficulty. Just over a year after writing to the Surveyor-General, on 17 November 1876, Russell wrote a despairing letter to Simms asking why he had not heard from him about the arrival of the ordered transit circle.8 He explained that the instrument was needed for the Trigonometrical Survey and for observations associated with the coming 1877 Mars opposition. He asked that the transit circle be sent at once, provided that did not make it faulty. The problem for Russell was that “… it puts me in such an unpleasant position here with the Government. So far all they know I have spent all the money, and there is not a single bit of the instrument to show for it.”
- 9 Gun metal is an alloy of copper, tin and zinc.
14The transit circle arrived in January 1877 (Wood, 1983). The description of the instrument here is based on what Russell provided in the first volume of results with the new instrument (Russell, 1881). It has a clear aperture of six inches (15 cm) and a focal length of 85 inches (2.16 m). The fittings of the object glass and the eyepiece are each attached to the smaller ends of symmetrical wrought brass cones. The larger ends of the cones are attached to the axis cube with the help of brass rings. The cube is 13-inch (33-cm) across on each side and connects the cones to the gun metal axis.9 The two 24-inch (61-cm) diameter circles are discs of cast brass with radial arms at the back and have graduations on silver to five minutes of arc; one circle is fixed and the other can be turned for test purposes. Two identical hollow piers support the telescope. For each pier the inner side is straight while the other three sides spread out towards the base, which is supported on stone. A system of counterpoise levers and rods with friction rollers reduce the weight on each Y that support the ends of the axis to only about seven pounds (3.2 kg). Figure 2 shows the transit instrument set up in the Observatory’s transit room together with the adjustable observer’s chair, the transit clock and the chronograph under a glass case to the left.
Figure 2 - The Sydney Transit Circle in its transit room c. 1890
Source: Powerhouse Museum, Sydney, Australia
15Through an arrangement of prisms, the circles are illuminated at points under the microscopes on each side by the same lamp that illuminates the wires in the eyepiece. Originally three sets of five wires were supplied with the instrument but Russell replaced them with a set of seven wires arranged to give an interval of about five seconds for an equatorial star. The eyepiece for star observations had a magnification of 145, while for observing the Sun a magnification of 100 was used; the latter eyepiece had a green filter away from the eye and an adjustable red one near the eye. For the convenience of the observer lying on the adjustable observing chair there were two seven-inch (18-cm) diameter setting circles near the eyepiece for approximate altitude adjustment of the telescope. Four ivory knobs allowed adjusting the brass tube without hands touching and heating the tube.
16As with all such instruments, a set of three instrumental errors had to be regularly measured and readings compensated accordingly. There are two collimators to obtain the collimation error. The north collimator is a 2.75-inch (7-cm) aperture telescope with a 33-inch (84-cm) focal length, placed on a massive sandstone pier outside the building. On the opposite side, the south collimator is a lens of four-inch (10-cm) aperture built into the external wall and focused on a silver plate with two small, engraved crosses 43 feet (13.1 m) away. First, the north collimator is aimed at the south one through an uncovered hole in the telescope cube and then the telescope is aimed at the two collimators in turn. The level error is determined by pointing the telescope downwards to a copper tray filled with mercury, the flat and horizontal surface of which provides a perfect mirror. This measurement is made with the help of a special eyepiece, called the Bohnenberger, which has a transparent diagonal reflector between the eyepiece and the wires. A lamp can then illuminate the wires so that both the wires and their reflection from the mercury, or more correctly, their shadow can be seen through the eyepiece. The final instrumental error, azimuth, was obtained from observations of the transits of stars with known positions from the Nautical Almanac.
17To facilitate the application of the measured collimation*, level* and azimuth errors* to observations, Russell commissioned the Sydney instrument maker, Angelo Tornaghi (1831-1906), to make two brass sliding scales: “… with these the error for the day being set at the zero of the scale, the quantity to apply is found opposite the star’s declination” (Russell, 1881, p. 13).
18After its arrival in January 1877, Russell quickly had the telescope set up and making observations. The first published observation was the right ascension of the star α Leporis (Arneb) made on 8 February 1877. Yearly star catalogues of right ascensions and north polar distances were produced containing 167 stars in 1877 and 254 stars in 1878. These were published in one volume in 1881 (Russell, 1881). The volume also contains a set of daily position observations of Mars and surrounding stars during its 1877 opposition; observations run from 25 July to 24 October. Another volume of yearly catalogues from the years 1879, 1880 and 1881, containing a total of 1737 star positions, was published in 1893 (Russell, 1893). The larger numbers of star positions obtained in the later years suggests increased familiarity and expertise with the use of the transit circle. The catalogues were for the use of the Trigonometrical Survey; however, it seems they were made available too slowly to satisfy the needs of the surveyors involved and relations between Russell and the staff of the Lands Department deteriorated in the 1880s (Orchiston, 1987).
19Observations with the transit circle continued after 1881, but the results were not published (Wood, 1958, p. 15). Russell may have lost some interest in the transit circle as he had designed a photographic version. He described his design of the proposed instrument, which did not eventuate, to a meeting of the Australasian Association for the Advancement of Science in January 1895 (Russell, 1895). Surprisingly, his design was in the form of an equatorial telescope in a massive English mount, that is, the telescope tube was to be supported on a frame between bearings on piers at the southern and northern ends of the mount.
20After Russell’s time at the Observatory, the emphasis of the work with the transit circle was on the determination of reference stars for the Astrographic Catalogue. The catalogue was a collaborative international project to photographically determine the position of stars over the entire sky (Turner, 1912). Sydney Observatory undertook to photograph and measure a large section of the southern sky (Wood, 1971). Position measurements of the stars needed a set of reference stars on each plate, with the position of the reference stars established through transit observations. A hierarchical system was involved in choosing and measuring reference stars: a relatively small number of fundamental stars, then a larger number of intermediate stars measured differentially from the fundamental stars and then much greater number of reference stars measured differentially from the intermediate stars. Using a fundamental catalogue of 1293 stars from the Royal Observatory at the Cape of Good Hope, Sydney Observatory prepared the Catalogue of 1068 Intermediate Stars (Cooke, 1921). Stars brighter than about magnitude 8.7 were observed with a moving wire micrometer, while for fainter stars the seven fixed wires were used. Reference star positions were then determined with respect to the intermediate stars. Eventually, there were insufficient resources to measure all the reference stars needed for the Sydney Zone of the Astrographic Catalogue and some of the needed star positions were taken from three catalogues from the La Plata Observatory, after adjustment for systematic differences (Wood, 1971, p. 18-19). These differences were established by comparing the 922 stars that were common to the La Plata catalogues and the Catalogue of 1068 Intermediate Stars.
21The transit circle continued to be used for time observations until the Observatory obtained a rubidium frequency standard in 1970 (Wood, 1981, p. 5). Then in June 1982, the New South Wales Government announced the termination of research at Sydney Observatory and the transfer of the building, the staff and the equipment to a large Sydney museum, the Museum of Applied Arts and Sciences (Wood, 1983). The transit circle became an exceptionally significant in situ static display (Kerr, 2002, p. 80). Initially, the instrument was on open display but, after some items such as some of the ivory knobs went missing, carefully designed glass walls were placed around it, forming a large display case. In 1993 a major conservation treatment was undertaken as the transit circle had by then endured over a century of the poor environment at the centre of a major city: dust, smoke and salt air, together with fluctuating temperatures and humidity (Ward, 1993). This was despite the piers and circles being protected by timber cabinets since the early 1900s. Exposed brass was treated by removing its lacquer coating and replacing it with a modern lacquer and tinting it to the original colour. A specialist paint conservator scraped a small patch from a painted area and found five layers of paint. Those painted areas of the instrument were then covered with Japanese tissue and painted with the best match to the original bluish colour, in a manner that is completely reversible.
- 10 William Simms, the sole proprietor of Troughton and Simms, died in 1860 (Turner, 1916). He was suc (...)
22Williamstown Observatory began in 1853 as a facility to provide time signals at the suggestion of Robert Ellery, a recent arrival in the Colony of Victoria from England, who had some astronomical experience at Greenwich Observatory (Gascoigne, 1972). Williamstown was only a few kilometres south-west of central Melbourne and had its own port; now it is a suburb of Melbourne. The first person put in charge of the facility soon resigned and Ellery was tasked with providing the time signal (Andropoulos, 2014, p. 53-59). In August 1858, Ellery was put in charge of the Geodetic Survey and Williamstown Observatory was transferred to the Crown Lands Department (Ellery, 1861). The following year, several instruments were ordered for the observatory to use for the survey, including a transit circle from Troughton and Simms. The foundations and piers were prepared in anticipation of the arrival of the instrument, though Ellery was concerned about their stability (Ellery, 1862a). He found slight movement in both azimuth and level, which he put down to the clay subsoil. He was even more concerned about the non-arrival of the transit circle from London. He stated that “The principal cause of this great delay has arisen from the death of Mr Simms, and the fact that Mr Simms, junior (who succeeds to the business), not being aware of the arrangements made with regard to payment, &c. ”.10 This was sorted out and the circle arrived in Melbourne on the ship Maxwell and reached the observatory on 17 August 1861 (Ellery, 1862b). As the piers were already prepared, the instrument was mounted and the first observations made with it within 10 days.
23Ellery described the transit circle in the introduction to the Williamstown Catalogue (Ellery, 1869) and in the introduction to the publication of the first results at the new Melbourne Observatory (Ellery, 1866). The description here is based on the latter publication. The object lens of the telescope had a diameter of five inches (12.7 cm) and a focal length of 72 inches (1.83 metres). The horizontal axis was made up of two cones of gun metal, at the ends of which were the pivots. The cones formed one casting together with the central cube of 10-inches (25-cm) width on each side. The pivots rested on brass Ys, one of which was adjustable horizontally, while the was adjustable vertically. A system of levers, counterpoises and friction rollers carried most of the weight on the pivots, leaving only 15 pounds (6.8 kg) to rest on the Ys. There was only one circle, of four-feet (1.22-metres) diameter, and with a silver ring, carefully engraved to five minutes of arc, on its outer face. Four microscopes were attached to the west pier, spaced 90° from each other, for reading the circle. These had micrometers with screw heads that could be read to a precision of one second of arc. For setting, the makers provided another set of five-minute divisions but more roughly engraved. Instead of making use of these divisions, Ellery had a six-inch (15-cm) setting circle, together with a spirit level, attached to the eye end of the telescope tube. The pre-prepared piers were made up of basalt blocks that rested on large blocks of the same material, which, in turn, were supported below ground on cemented gravel. Figure 3 shows a diagram of the instrument.
Figure 3 - Drawing of the Williamstown Transit Circle
Source: Museums Victoria Collections
24Collimation error was found with the help of two collimation telescopes of 2.75-inch (7.0-cm) aperture and 33-inch (84-cm) focal length. These were mounted inside the transit room on heavy stone piers. The first step in using them was to point them at each other through an uncovered aperture in the cube of the transit circle. Once these were adjusted to be in alignment, the telescope was pointed at each collimation telescope in turn and readings taken of the position of the right ascension micrometer when the central wire was in the collimation or rotation plane of the instrument. Some corrections were then made, including for the very small diurnal aberration, the short delay from the true time in the transit of a star of about 0.02 seconds due to the speed of rotation of the Earth at the latitude of Melbourne. Collimation error was generally determined every 10 or 15 days.
25The other two standard transit errors, that of level and azimuth were determined for every set of readings. Level error was found, as was usual, by pointing the telescope downwards with a Bohnenberger’s eyepiece and matching the direct view of the central wire with that of its reflection. The reflection was from mercury held in a round container that was suspended by an elaborate system of India or natural rubber bands to reduce vibration. Azimuth error was found by observing circumpolar stars: either by comparing a star near the pole with one near the celestial equator or a star above the pole was compared with one below. Prior to observing the transits of each star for this purpose, corrections were made for collimation and level errors.
26Ellery and his assistant astronomer, Edward John White (1831-1913) (Anonymous, 1914; Tebbutt, 1913), began observing with the transit circle soon after its arrival at Williamstown Observatory. It was used for time observations, the determination of the geographical coordinates of the observatory and a program of measurement of stars to the sixth magnitude was commenced (Ellery, 1862b). By May 1862, 3774 right ascension observations had been made together with 2129 north polar distance measurements.
27Also in 1862, Ellery and White joined with the Royal Observatories at Greenwich and at the Cape of Good Hope to observe the opposition of Mars (Stone, 1865). Comparison of the observations from the three observatories, when analysed at Greenwich, yielded a value of 8.943 arc seconds for the solar parallax, equivalent to 147.1 million km for the distance of the Sun. This value was in good agreement with that found by other contemporary astronomers, though it was somewhat higher than the currently established value of 8.794 arc seconds or 149.6 million km for the solar distance. The discrepancy in the 1862 value is unsurprising as systematic errors were likely due to the red colour of Mars (Spencer Jones & Halm, 1925). There would have been confusion with the chromatic dispersion of the atmosphere, as well as a difference between the planet’s colour and that of the comparison stars used.
28Eventually, Ellery (1869) collected all the observations made at Williamstown, before the move to the new Melbourne Observatory, that is, from the years 1861, 1862 and 1863, and published them as the Williamstown Catalogue. According to the Mount Stromlo Observatory astronomer, Ben Gascoigne (1992), “It was a timely publication that received much favourable comment overseas.”
29In 1863 a new Melbourne Observatory was established at a better site, with Ellery again in charge. Meridian observations continued there, with White having responsibility for observations with the transit circle and their reduction. Results were published every few years and then collected together into a general catalogue: the First Melbourne Catalogue of 1227 stars (Ellery, 1874), including observations from 1863 to 1870 and the Second Melbourne Catalogue of 1211 stars (Ellery, 1889), including observations made from 1871 to the middle of 1884, contain observations made with the Williamstown transit circle. These catalogues were appreciated; like Russell, Ellery travelled to England in 1875 and the two Australian astronomers were present at a dinner to celebrate the Bicentennial of the Greenwich Observatory. There, the Astronomer Royal, George Airy (1801-1892) said that, “… the Melbourne Observatory has produced the best catalogue of stars of the Southern Hemisphere ever published” (Ellery, 1876). This public praise was for the First Melbourne Catalogue that had been then recently published. White, by now designated First Assistant, not only had made the observations in the second catalogue but had also undertaken the reductions and the preparation for publication of the catalogue. The introduction of that catalogue explains that originally it was planned to include only observations to the end of 1880. However, with the arrival and installation of the new transit circle in 1884, it was decided to extend the catalogue to August of that year, when observations with the Williamstown transit circle were discontinued.
30After catalogue work with the instrument stopped, it seems that it was still used occasionally under the name, the West Transit Circle. The 1909 report of the observatory (Baracchi, 1909) states that, “The 5” West Transit circle is not used for systematic work at present, but the instrumental errors have been determined periodically, and 50 observations of clock stars and 98 of circumpolar stars were obtained.” The instrument can no longer be located and its fate is unknown (Clark, 2007 p. 142-143).
31In 1875 Ellery travelled to England and took the opportunity to also inspect observatories in Brussels, Paris, Strasbourg and Berne. He found that Melbourne Observatory was equipped as well as the ones he saw, except for the small aperture of the transit circle. This led to Ellery to start agitating for a more modern instrument with a larger aperture to allow fainter stars to be observed (Ellery, 1876). The new, larger-aperture transit circle arrived at Melbourne Observatory in May 1884 (Ellery, 1884). The difficult task of installation in a new, purpose-built transit room was finished on 7 July of the same year. Then it took until 22 August to complete the necessary steps, platforms and observing chairs (Ellery, 1885). The instrument, made by Troughton and Simms, has an aperture of eight inches (20 cm) and a focal length of 108 inches (2.74 m). Its description here is based on that of Ellery (1884) in his 1884 report to the observatory’s Board of Visitors. The telescope is carried on an axis of 52-inch (1.32-m) length with steel pivots of 4.5-inch (11.4-cm) diameter. There are two 3-foot (91-cm) wide divided circles on the axis, one of which is fixed, while the other can be rotated. The circles are made of gun metal and can be read through a reading telescope and four microscopes.
32A major innovation with this instrument aimed to prevent the flexure of the axis, to which similar large transit circles were prone (Ellery, 1884; Atkinson, 1967). The usual arrangement, as with the Williamstown transit circle, was for the axis to be made up of a single casting of a central cube with cones on either side. Instead, here the cube has been replaced with a cylinder that is crossed by another to hold the eye and objective ends of the telescope. This was a difficult form to make and, as a result, there was a year’s delay in the delivery of the instrument. James Simms of Troughton and Simms told Ellery that, “… he found the result very satisfactory.” Despite the different form of the casting, the usual opening is present in its centre, so that the two 6-inch (15-cm) aperture collimation telescopes could be visible to each other. Figure 4 shows the Melbourne transit circle.
Figure 4 - The Melbourne Transit Circle
Source: Museums Victoria Collections
33By the time of the next annual report (Ellery, 1885) the new transit circle was fully operational. Ellery relates that, when in use, the observer frequently needed to record the outside temperature and hence had to run outside each time. To improve the situation and allow the observers to record the temperature from inside the transit room, Ellery had a thermometer placed about 50 feet (15 m) from the building and arranged for it to be read by means of a telescope fixed to a door. An incandescent bulb powered by a battery inside the transit room provided the illumination for reading the temperature. Another change was in the mercury bath used to observe the nadir* and obtain the level error. With the old (Williamstown) transit circle there was no problem with the system in which the bath was suspended by an arrangement of natural rubber bands. With the new, larger instrument, it was found that there were minor disturbances in the surface of the mercury that prevented readings being taken (Ellery, 1886a). To mitigate this, Ellery adopted a system from the Paris Observatory, in which the mercury bath is partially allowed to float within another. The new system successfully allowed observations, as any disturbances were quickly dampened (Ellery, 1886b).
34The Third Melbourne General Catalogue (Ellery & Baracchi, 1917) contained the first decade of observations with the new transit circle, that is, the period from 1884 to 1894. Due to the Depression of the 1890s and the lack of funding from the government, the catalogue was not published until 1917, by which time Ellery and White had both long retired and the publication of the catalogue was supervised by Italian-born Pietro Baracchi (1851-1926), the new Government Astronomer (Perdrix, 1979). The 3068 stars in the catalogue came from four different lists, with each list of stars observed for different purposes: stars with well determined positions to determine clock error and the azimuth error of the transit circle, reference stars for the Melbourne and the Mexican Astrographic zones, stars used in connection with comet observations and stars requested by international authorities and astronomers. Reference stars were needed for the Astrographic Catalogue project as, like Sydney Observatory, Melbourne Observatory had accepted a large zone of the southern sky to catalogue through photography. As well, the observatory assisted Tacubaya Observatory in Mexico by supplementing the reference stars for the Mexican zone. No further general catalogues were published by Melbourne Observatory, though a fourth was published, after the observatory had ceased operating, at Mount Stromlo Observatory in Canberra in 1959 (Gascoigne, 1992). Melbourne Observatory closed as a research institution in 1944 and little systematic work was done with the transit circle in its last few decades. A 1931 newspaper article pictured the last Government Astronomer, Joseph Baldwin (1878-1945) with the instrument and the caption stated that, “This instrument is used periodically to determine the correct time” (Anonymous, 1931).
35In 1947 the Melbourne Transit Circle was presented by the Victorian Government to the Astronomer Royal, Sir Harold Spencer Jones (1890-1960), when he was visiting Melbourne (Clark, 2007). The instrument was sent to the Royal Observatory, Greenwich but not mounted there until March 1978. Later that same year, it was returned to Melbourne and is currently in storage at Museums Victoria.
36Nineteenth century astronomers at Sydney and Melbourne took their responsibilities to observe the southern sky seriously. At the early Parramatta Observatory, just outside Sydney, a transit circle was only received in 1835, 13 years after it was established. This was a transit circle by Jones, which was an early attempt to merge the two separate instruments of a transit telescope and a mural circle. It was little used due to its poor quality; a quality compounded by the difficulties posed by the distance of the observatory from its maker. Although, it was sent back to England for repair prior to its installation at the new Sydney Observatory, it was never an accurate instrument.
37Williamstown Observatory was more fortunate in the transit circle it received from Troughton and Simms in 1861, as it was a solid and useful instrument. It, and the similarly designed but slightly larger Sydney Observatory transit circle of 1877, were obtained due the demands of the geodesic or trigonometrical surveys of their respective colonies. Hence, the main initial effort of the astronomers with the two instruments was in obtaining star positions for the two surveys. Star positions were published regularly with both transit circles, though the work with the former is better known due to the compilation of its results into the Williamstown and the First Melbourne General catalogues. Eventually, in 1884, the Williamstown instrument was replaced at Melbourne Observatory with a larger transit circle, again from Troughton and Simms, but with a new and improved design giving reduced flexure.
38Ellery and White at Melbourne and Russell and his assistants at Sydney, all showed great skill in operating their respective transit circles and carrying out the necessary reductions to reach publishable results. They showed themselves masters of the complex and yet tedious corrections needed to ensure accuracy. These corrections included the three standard instrumental errors discussed in this paper, collimation, level and azimuth, as well as others such as, division errors, flexure errors, clock errors, personal equations, refraction, curvature and diurnal aberration. They succeeded at this work despite the afore mentioned distance of Australia from Europe and the consequent rare, if any, opportunities to interact with their colleagues elsewhere.
39One of the reasons that Russell and Ellery succeeded was that they modified their transit or meridian circles for the circumstances of their observing conditions and the convenience of the observers. Instances being, as previously related, that Russell designed two brass sliding scales to speed up the calculations of the necessary corrections to positions observed with the Sydney transit circle and built the south collimator into an external wall. Others examples are that Ellery made innovative arrangements to read the temperature needed for the reduction of observations with the Melbourne transit circle from inside and constructed an elaborate system to preserve the smoothness of the mercury bath. Thus they formed assemblages of telescope and observer.
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