We will be discussing the history of the specification and definition of some of the most important standard measuring units (just for starters: our standards of length, time, and mass), and the history of the measurement and determination of associated physical constants. The U.S. National Bureau of Standards (new name, National Institute of Standards and Technology) was established for this purpose, and has recently celebrated its centennial:

National Institute of Standards and Technology
http://www.mel.nist.gov/div821/index.htm
http://www.mel.nist.gov/div821/museum/length.htm
http://www.mel.nist.gov/div821/museum/timeline.htm

NIST Centennial -- National Bureau of Standards
http://www.100.nist.gov/
http://museum.nist.gov/exhibits/index.html

The Bureau International des Poids et Mesures (BIPM) is in Paris (http://www.bipm.fr/) and "operates under the exclusive supervision of the International Committee for Weights and Measures (Comité International des Poids et Mesures, CIPM), which itself comes under the authority of the General Conference on Weights and Measures (Conférence Générale des Poids et Mesures, CGPM)."

For a current statement of the Standard International (SI) system of units, as established by the CIPM and periodic meetings of the CGPM, see: http://www.physics.nist.gov/cuu/Units/current.html. The SI system encompasses seven fundamental basic units; of (1) length (the meter), (2) mass (the kilogram), (3) time (the second), (4) electric current (amperes), (5) thermodynamic temperature (degrees kelvin), (6) quantity of substance (the mole), and (7) luminous intensity (the candela). The standard units for plane angular measure (the radian) and solid angle (the steradian) are dimensionless and are characterized as "supplementary" units in the SI system.

In discussing the SI system, we can talk about differences between "artifact standards" (e.g., the original standard meter bars in Berlin and Paris; the standard kilogram in Paris is still used as the international artifact standard for mass) and the use of assumed physical invariants (e.g. the current definition of the meter as unit distance traveled by light in one very small fixed unit of time).

In discussing the definitions and determinations of associated physical constants, I suggest that we focus on:

* the speed of light, both via direct measurement and via Maxwell's equations
* the constant of gravitation and standard measures of acceleration due to gravity
* the Planck constant and Planck units of mass, length and time
* the fine-structure constant and its role in current standard cosmological models
* the Hubble constant (or "Hubble parameter") and age of the universe

Three recent books that might make for interesting reading in advance of our meeting are Ken Alder's recently-published "The Measure of All Things" (the story of the meter, which should be available from most good public libraries), Martin Rees' "Just Six Numbers" (key parameters of the standard model), and a collection of historical essays on 19th century scientific practice, "The Values of Precision" (M. Norton Wise, ed.).

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The Measure of All Things: The Seven-Year Odyssey and Hidden Error That Transformed the World.
Ken Alder. x + 422 pp. The Free Press, 2002. $27.
http://www.americanscientist.org/bookshelf/Leads03/bookshelf0303.html
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The Values of Precision
Princeton University Press (1997)
Edited by M. Norton Wise
http://pup.princeton.edu/titles/5600.html