Where are and where were magnetic fields measured in Australia? Are old numerical records worthwhile?

Melbourne Observatory_Nick Lomb

The main buildings at Melbourne Observatory. Image and copyright Nick Lomb ©, all rights reserved

Question from Harry R: A 2006 article by David Hathaway says that terrestrial magnetism is measured at two points on Earth – in UK and Australia.

Where would that be Nick – do you know?

Answer: That is an interesting question Harry. The search for an answer led me on a fairly convulated path that I try to summarise below. Sydney Observatory made magnetic observations for a few decades in a hut built on the meridian at the northern end of its grounds. These observations had to stop once electric trams began running in the vicinity. As far as I am aware the Sydney observations are unpublished.

David Hathaway is talking about the aa index that is used to estimate the effect of the wind of charged particles from the Sun on the Earth’s magnetic field.

Geoscience Australia says that the aa index is based on measurements at “two antipodal subauroral stations: Canberra Australia, and Hartland England.” The Canberra station they refer to is the Canberra Magnetic Observatory in the Kowen Forest ACT. However, that observatory has only been operating since 1979. Where were the measurements taken previously?

A different Geoscience Australia webpage tells us that the first magnetic observatory in Australia operated at Hobart from 1840 to 1854. Magnetic readings were then continued at an observatory set up by the German scientist Georg von Neumayer at Flagstaff Hill in Melbourne.

In 1862 the observations were transferred to the new site of Melbourne Observatory near the Botanical Gardens in 1862. The aa index is taken from data back to 1868. Dr Barry Clark (unpublished, 2007) says that self-recording magnetic instruments were ordered for Melbourne Observatory in 1866. So presumably the start of the aa index is when those instruments arrived and began producing results.

Barry Clark also mentions that in the 1890s Melbourne Observatory had to curtail its operations due to economic considerations. The then director decided that the magnetic observations had to continue in order to maintain the unbroken series of measurements. Instead he cut back on the publically much higher profile programs in meteorology, observations with the Great Melbourne Telescope and public telescope viewing. This was a brave and farsighted decision.

In the 1900s, as at Sydney Observatory, the introduction of electric trams made magnetic measurements difficult from Melbourne. A new site for magnetic observations was set up at the small town of Toolangi, which is about 50 km to the north-east of Melbourne, and just to the north of Healesville. Measurements continued there, even after the closure of Melbourne Observatory in the 1940s, right up to the opening of the Canberra Magnetic Observatory in 1979.

So the short answer to your question Harry is Melbourne-Toolangi-Canberra.

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3 responses to “Where are and where were magnetic fields measured in Australia? Are old numerical records worthwhile?

  • While the history of magnetic observations from Australia has a long standing record, including the first in Tasmania in 1792/3 and then at Parramatta Observatory in the 1820s. The divide of course was the famous Carrington’s 1st September 1859 magnetic storm, where the greatest magnetometer deviation so far observed. It must have frightened the heck out people and the scientific community at the time, even though this wasn’t understood until much later! (IHV reached around 110 nT!) Hence why; Hathaway says “…IHV data have been taken every day since 1868,…”

    One of the most important of the magnetic observations in the south, of course, were made by the French physicist Elisabeth Paul Edouard de Rossel at Recherche Bay in 1792 -1793. He did pioneered work of of geomagnetism, and was first to prove geomagnetism varied with latitude.

    The mission of course was to look for the ill-fated mission at La Perouse in 1788. (Had the ship and records not have been lost, the first astronomical ‘observatory’ and astronomical work may have been actually had been made at Botany Bay. (Jupiter’s moon observations, I think, is mentioned by Dawes.)

    As for the first geomagnetic observations of note was made by him during the d’Entrecasteaux expedition. The scientific observatory was used in April 1792 for 26 days, and again in January 1793 for 24 days .[1] (See http://www.environment.gov.au/heritage/publications/about/pubs/national-heritage-recherche.pdf )

    According to the Tasmanian Heritage Council, to and to directly quote from them;

    “On 14 February, Labillardiere (1800: 315) notes in his journal that “…a great number of observations made on board gave us the variation of the needle 734 east, while at the observatory we found only 255 east variation. A difference so great must unquestionably have arisen from some magnetic point”; (Labillardiere 1800: 314-315). As a result of the shore-based observatories, the journal of d’Entrecasteaux noted that the longitude of this port has been fixed from the results of a great number of distances of the moon to the sun (Duyker and Duyker, 2001:150). ”

    Also Mulvaney (2007) [2], says;

    “Elisabeth Paul Edouard de Rossel (1765-1829) reported six magnetic
    intensity measurements performed by timing 100 oscillations
    of a vertical dip needle (Figure 8) [de Rossel, 1808].
    These measurements, performed between 1791 and 1794 with
    consistent instruments and methods, near 48 deg. N, 28 deg. N, 3 deg, S, 7 deg. S, and 43 deg. S, the latter in Van Diemen’s Land in Tasmania, allowed de Rossel to conclude;

    “By comparing the experimental results obtained during the expedition with each other it is evident that the oscillations of the needle were more rapid at Paris and Van Diemen&8217;s Land than at Surabaya in the Isle of Java and at Amboyna; and that therefore the magnetic force is greater near the poles than at the equator.”

    Sadly much of this original work has not come to light, but the extensive records of the French Admiralty, who used his geographic and hydrographic information to great advantage for their own expeditions.

    Cheers

    [1.] A good reference for this is Clode, Danielle., “Voyages to the South Seas: In Search of Terres Australes&8221;, Pub. Miegunyah Press,
    Melbourne (2006)
    [2.] Mulvaney, D.J., “‘The axe had never sounded’; : place, people and heritage of Recherche Bay.”;, ANU, EPress (2007)

    • Thanks Andrew. Fascinating stuff. I did write a previous post on this blog on the dip circle from Parramatta Observatory that was used for measuring the intensity as well the dip of the magnetic field.

      • > Yes I’ve read Sharon Ruttlidge’s paper in the Royal Society Journal recently, and ‘re-discovery’ of this dip circle. (It also saw it on the ABC News.)

        Magnetometers like this are commonplace in some areas of the world. Amateur ones are the so-called via so-called ‘jam-jar magnetometers’, which can be used as an aurora alerts. (A great kids experiment.)

        The 1859 event was observed through SE Australia [1], and articles can be found at the NLA’s (National Library of Australia ‘Trove’, showing many of the newspaper reports at the time. (A listing is at; http://trove.nla.gov.au/newspaper/result?q=Aurora&l-decade=185)
        The most remarkable descriptions were the by John MacDonald [2], who view this aurora from Wynyard-square (Wynyard), after walking fro Market Street to York Street looking for a fire until it dawned on him it was an aurora.

        More incredibly he describes;

        “That it is a luminous magnetic cloud, produced by meteorological causes, appears evident from the fact that the telegraphic communication along our wires was interrupted during its existence. We can easily imagine the powerful magnetic cloud floating over our colonies, pressing upon the telegraphic wires, attracting and extracting from them the current of electricity at those periods when the fact became remarkable.” [2]

        The first recording I’ve found of an aurora australis observations from Sydney seems to have in 1847, which was noted from a little east of Macquarie Street in the Botanical Gardens.

        I also known that John Tebbutt had a dip circle after this event 1859, and some of his observations were published too.

        [1] THE AURORA AUSTRALIS. To the Editor of the Sydney Morning Herald.
        The Sydney Morning Herald (NSW : 1842-1954) Thursday 1 September 1859 p 5 Article By John Tebbutt.

        [2] AURORA AUSTRALIS. To the Editor of the Sydney Morning Herald.
        The Sydney Morning Herald (NSW : 1842-1954) Thursday 8 September 1859 p 8 Article BY JAMES MACDONALD.

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