M E D IA  R E L E A SE: T o d' NEW  DEFINITION OF THE METRE 83-305The M inister fo r Science and Technology, Mr Barry Jones, announced today that Australia is  changing its  legal d e fin itio n  of the metre. This follows a recommendation by the National Standards Commission that the Commonwealth Weights and Measures Regulations be amended to incorporate a d e fin itio n  agreed to in Paris on 20 October 1983 by the 17th General Conference of Weights and Measures.The new d e fin itio n  is :The metre is  the length of the path travelled by lig h t in  vacuum during a time in te rv a l of 1/299 792 of a second.Australia was represented at the General Conference by the Chairman of the National Standards Commission, Dr W  R Blevin, in his capacity as Chief Standards S cientist with the CSIRO Division of Applied Physics, and had supported th is  fundamental change to the international system of units.Mr Jones emphasised that the length of the newly defined metre is  not detectably d iffe re n t from that of the previous metre, which was defined in terms of the wavelength of the orange coloured lig h t emitted by krypton atoms. Consequently, the new d e fin itio n  does not necessitate any change to existing practices in everyday measurement and engineering. I t  does enable the length of the metre to be established much more precisely, however, and at the same time i t  provides an exactly known value fo r the speed of lig h t. These factors are of considerable advantage to several fie ld s  of science, such as astronomy, geodesy and spectroscopy.Mr Jones pointed out that a further advantage of the new d e fin itio n  is  its  conceptual sim p licity allowing i t  to be more readily understood by students and others.The CSIRO Division of Applied Physics, which has the re sp o n sib ility of maintaining A ustralia's primary standards of measurement, made sig n ifica n t contributions to the international research collaboration that led to the new d e fin itio n . The Division has already established a new primary standard of length in  order to exploit the advantages of the Ã¢ÂÂ¢ new d e fin itio n . This involves a sophisticated helium-neon laser em itting red lig h t, the frequency and wavelength of which are stab ilised by reference to the absorption spectrum of iodine vapour.For further de tails:Eric Hunter Director, Public Relations (062) 64 4145 (B)51 3657 (H) .December 1983The Hon. Barry O. JonesiUinister forScience ami Technology

