Measures for Progress: A History of the National Bureau of Standards

464 THE NEW WORLD OF SCIENCE (1946-51)
Dr. lie ggers observing the spectral line of the mercury isotope of mass 198, a potential
basis for an atomic standard of length.
German successor to the PTR), and in October 1960 the krypton lamp was
adopted as a new international standard of length.98
Other developments in the postwar period, discussed later in the
section on nuclear physics, included a standard of time, determined by an
atomic clock; a primary neutron standard; and a fundamental nuclear con-
stant, the gyromagnetic ratio of the proton.
Much new work was done in the field of physical constants. The
Bureau made available comprehensive data on the infrared
spectra of chemical compounds for use in research analysis. It compiled
tables of selected values of chemical thermodynamic properties for the simple
sulfur compounds and the compounds found in liquefied petroleum gases.
R. L. Barger and K. G. Kessler, and atomic-beam-emitted Hg198 wavelengths,"
J. Opt. Soc. Am. 51, 827 (1961). -
In possible extenuation of the European adoption of the krypton lamp was the fact that
at that time only the United States had reactors to supply mercury 198 (interview with
Dr. Condon, Oct. 29, 1963).
Objective comparisons made in neutral laboratories reportedly agreed in general that
krypton provided the highest precision. Despite the krypton lamp standard, metrology
and spectroscopy laboratories both here and abroad use the Meggers lamp for its com-
bination of accuracy and simplicity. Laser sources may yet supersede the atomic beam
principle as the ultimate in sharpness in a spectral line standard. Interviews with Dr.
Meggers, Mar. 13, 1962, and July 7, 1964; A. G. McNish, "Lasers for length measure-
ment," Science, 146, 177 (1964).