Announcement from USMA, in case any of you can attend: Here is an announcement just received from NIST for an upcoming seminar at NIST September 15, 2009 (see below). You may contact William Anderson, the host, who will register guests as visitors to NIST. Elizabeth Gentry can assist with registration if William Anderson is unavailable. [email protected]<mailto:[email protected]>, 301-975-3690 Elizabeth J. Gentry National Institute of Standards and Technology Weights and Measures Division Laws and Metric Group 100 Bureau Drive Stop 2600
Gaithersburg, Maryland 20899-2600 301-975-3690 Fax: 301-975-8091 http://www.nist.gov/metric 9/15/09 10:30 AM - MSAG SEMINAR: The International System of Units, the SI: Future Changes Planned for the Definitions Administration Bldg, Green Auditorium. (NIST Contact: William Anderson, 301-975-8280, [email protected]<mailto:[email protected]>) "Metrology is the science of measurement. Our ability to make reliable measurements of all kinds is essential to science and technology, and to much of our every-day life. It is the responsibility of the National Metrology Institutes (NMIs, such as NIST, NPL, PTB, NMIJ, CSIRO etc.) and particularly the Bureau International des Poids et Mesures (the BIPM) to provide and maintain the International System of Units (the SI) for the world. It is easy to think of this as a trivial operation, but it is not: It is fundamental for the life we wish to lead, as the speaker shall show with examples. The history of the SI will be described, from its inception in 1790 when Louis 16th established a commission to choose units for the world, to the many changes of the last 50 years. The successive definitions of the seven base units, the metre, the second, the kilogram, the ampere, the kelvin, the mole, and the candela, will be described. The metre has been revised four times, from its definition as one ten millionth of a quadrant of the earth (1793), to the distance between the defining scratches on the prototype metre bar (1895), to a multiple of the wavelength of the red krypton atomic line (1960), to the distance light travels in vacuum in a specified time interval (1983, and still the current definition). The second was originally defined astronomically in terms of the period of rotation of the earth, but is now defined as a multiple of the period of the microwave hyperfine transition in the caesium atom. The kilogram was originally defined as the mass of a decilitre of water, but since 1895 it has been – and still is – defined as the mass of the international prototype of the kilogram, made of platinum-iridium, kept at the BIPM. But we know that the prototype kilogram is itself changing in mass. Of the seven base units, at least five will be given new definitions within the next few years." Ian Mills , President of the CIPM's CCU, University of Reading.
