Session X2: Invited Session: History of Metrology and Today's Frontiers of Measurement

Dreams of a Final System: Origins of the Quest for an Absolute Standard

The first attempts to find unchanging phenomena that could be used to evaluate the accuracy of standards and recreate them if lost predated the metric system. As early as the seventeenth century, members of the French Academy and British Royal Society sought to use the seconds pendulum and the Earth's meridian as tethers for length standards. These efforts ultimately failed. The vision of an absolute standard was revived in the 1870s, when C. S. Peirce was the first to experimentally tie a unit, the meter, to a natural standard, the wavelength of a spectral line, using a diffraction grating. This work inspired A. Michelson and E. Morley, in the 1880s, to apply the interferometer with which they were attempting to detect ether drift to this purpose. Michelson further pursued this work at the BIPM in 1892, which set the stage for the later redefinition, in 1960, of the meter in terms of the wavelength of a spectral line.   

Beller Lectureship: From Artefacts to Atoms: The Origins and Early Years of the International Bureau of Weights and Measures (BIPM)

The BIPM was founded by the Metre Convention in 1875. Its main task was to maintain and disseminate the units of length and mass using the new International Prototypes of the Metre and Kilogram. My talk will be based on the opening chapters of my book ``From Artefacts to Atoms'' which recount the story of the Metre Convention and the creation of the BIPM at the Pavillon de Breteuil in S\`{e}vres on the outskirts of Paris, as the first international scientific institute. I shall include a brief outline of the sometimes acrimonious discussions at the Diplomatic Conference of the Metre, which opened on 1 March 1875 and concluded with the signing of the Convention on 20 May, of the construction of a new laboratory building, recruitment of staff, purchase of instruments and equipment and the beginning of scientific work. There was no precedent for any of this, success was due to the wisdom and foresight of those who drafted the Convention and to the founder Members of the International Committee for Weights and Measures overseeing the BIPM and to the high quality of the original scientific staff. However, success came at a price, the decision to define the Metre at 0 $^{\circ}$C, for example, led to much ill health in the early years among the staff from working in cold damp laboratories, an aspect of metrology that is easy to forget these days.   

Measurement of the gravitational quantities g and G: How ideas for precision measurement experiments come about

I will talk about g and G whose determinations go back to some of the earliest measurements in the history of metrology. Although today's measurement accuracy for g, the free-fall acceleration due to the Earth's gravity, has improved by nearly nine orders of magnitude, the measurement accuracy of G, the Newtonian Constant of Gravitation, has improved by only two orders of magnitude over its 300 year measurement history. I will discuss what has driven (and impeded) this progress, and how ideas for improvements in these measurements have helped advance the frontiers of measurement science. Finally, I will point out the interconnectedness of all precision measurement experiments.   

The Odyssey of the Frequency Measurements of Visible Light at NBS/NIST

The long term goal of defining the length standard based on a constant of nature rather than an artifact was pursued at the National Bureau of Standards/National Institute of Standards of Technology during the period of 1968 to 1983. With the invention of the laser it became possible to measure the frequency of lasers, stabilized on atoms or molecules, with the cesium atomic clock as the time standard. Using lasers, high speed MIM (metal insulator metal) diodes, and summing the radiation from three lasers in a He-Ne plasma the frequency of the iodine stabilized HeNe laser at 633 nm was measured by direct frequency counting to an accuracy of 1.6 parts in 10$^{10}$. The major consequences of this accomplishment were the adoption of a fixed value for the speed of light and the redefinition of the SI meter based on the speed of light. After a brief historical review, the milestones of the research will be outlined and the principle researches indicated.   

Evolving Planck Constant Measurements into the SI Kilogram Standard

This is a very brief 100 year history of measuring 2$e$/$h$ (pre-and post-Josephson), with a little on $e^{2}$/$h$ (quantum Hall Effect, QHE), and then on to a direct measure of Planck constant $h$, where the watt balance technique combines four basic standards, i.e., physical constants of time, length, voltage, and resistance into a mass redefinition. There are parallels between old and new controversies. In the 1970's and 80's the controversy was in the changeover from standard cells to the Josephson effect as voltage reference. A slightly similar and briefer one concerned the ohm and QHE. Today's discussion is about changing definitions from an artifact mass standard to the Planck constant (or Avogadro constant) using the different methods as realization. The mass redefinition concerns are two orders of magnitude down from those of voltage, and the discrepancies between $h$ are probably more systemic rather than artifact related (or not) as compared to the Josephson effect testing. This shows how far electronic metrology has progressed but also that is it not completed research. The conclusion summarizes the latest efforts on the watt balances.