Scale Model Studies of a Transient Electromagnetic Prospecting System Using an Interactive Minicomputer
Scale models have been used for over thirty years in studying the electrical and electromagnetic techniques of geophysical prospecting, and are particularly useful when mathematical or numerical methods are unreasonably difficult. A model study facility has been set up at Macquarie University, Sydney, Australia, to study the transient electromagnetic method of geophysical prospecting. The basic unit in the facility consists of a 35Kword INTERDATA minicomputer which controls the timing and waveform of the transmitted pulse as well as subsequent data collection and processing. A wide-band amplifiler provides an interface between the computer and the small multiturn loops used for model studies. Input and output data are fed via the computer to a teletypewriter. The use of an interactive technique between the computer and operator enables optimum timing and amplifier settings to be easily determined for each model. A model of a uniformly conductive half-space was used to validate the experimental arrangement, and excellent agreement was found between theoretical and model results. A model study of an orebody enabled estimates of bulk conductivity to be made.
Time Domain EM Comes to Australia: the Early History of the MPPO-1
Australia, with its extensive ancient and weathered terrain, has long been a testing ground for geophysics. The Imperial Geophysical Experimental Survey (I.G.E.S) carried out 18 months of fieldwork in Australia during 1929–30 ‘for the purpose of conducting thorough trials of the principal geophysical methods to determine their practical value and limitations under a variety of geological conditions’ (Broughton Edge and Laby, 1931). Between 1935 and 1940 the Aerial, Geological and Geophysical Survey of Northern Australia (AGGSNA) used the latest aerial, geological and geophysical techniques to map and explore remote areas of Northern Territory and Queensland, and this led to the establishment of the Bureau of Mineral Resources, Geology and Geophysics (BMR) in 1946. For more than half a century Australia has proved a challenging and fruitful frontier for testing the latest geophysical technology.
Time and Heritage
As a historian studying what can be considered a form of intellectual history, I have slowly come to adopt Michel de Certeau’s observation made at the end of the 1980s that ‘objectifying the past, for the last three centuries, has undoubtedly left unconsidered time within a discipline that has continued to use it as a taxonomic instrument’. To a certain degree, time has become commonplace for the historian who has preserved or instrumentalized it. It is not considered because it is inconceivable, but because we do not think of it or, more simply, we do not think about it. As a historian attempting to pay attention to the time I’m living in, I have thus, like many others, noticed the swift development of the category of the present until it has become obvious that the present is omnipresent. This is what I refer to here as ‘presentism’.