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

336 THE TIME OF THE GREAT DEPRESSION (1931-40)
was hoped that with acceptance many of the difficulties in the way of inter-
national interchangeability of parts in industry might be satisfactorily solved.
No serious competitor of the cadmium red line had been found since
Michelson's comparison of that wavelength with the international meter in
1893. Now, in the light of advances in spectroscopy, the search for possibly
superior lines was renewed. The arc and spark spectra of the elements kryp-
ton and xenon disclosed very narrow lines when subjected to low temperatures
obtained with liquid air, though none compared favorably with the cadmium
lamp line.109 For its own purposes, however, the Bureau developed a method
for the use of cadmium and krypton wavelengths in the measurement of
master precision gage blocks that permitted their certification to an accuracy
of 0.000001 inch per inch or three times closer than Not until
after World War II were krypton and mercury lamps devised that made
possible a redefinition of the light wave to give more precise values for the
inch and yard.
Earlier, in 1932; as a matter of industrial convenience, the Bureau
and the American Standards Association agreed on a new ratio between the
American inch and the millimeter. Arbitrary reduction by 0.00005 milli-
meter in the American inch made its equivalent to the 25.4-mm inch that was
standard in England, and the new agreement put precision measuring in the
two countries on the same basis, with consequent advantage to American
export industries.11'
Because the national laboratories both here and abroad had fewer
calls on them from industry, the depression years were remembered as a
time of international conferences, of many interlaboratory comparisons and
exchanges of data and equipment looking to new or improved international
standards. Besides the work in thermometry and standards of length, much
was done in the standards upon which electrical, heat, photometric, X-ray,
and radio measurements depend."2
100 NBS Annual Report 1928, pp. 2—3; Annual Report 1929, p-8.
For the earlier research see S441, "Notes on standard wave-lengths, spectrographs, and
spectrum tubes" (Meggers and Burns, 1922); Meggers, "Measuring with light waves,"
Sci. Am. 129, 258 (1923) and Sci. Am. 134, 258 (1926); S535, "A fundamental basis for
measurements of lengths" (Bearce, 1926).
110 NBS Annual Report 1935, pp. 66—67. The early work on standardization of precision
gages was done on the Hoke blocks of World War I (ch. IV, p. 200) and reported by
Peters and Boyd in S436 (1922) -
" Science, 76, supp. 8 (1932). See app. B.
" NBS Annual Report 1929, pp. 2—3, marks the first appearance of a series of yearly
notes on interlaboratory cooperation and on international visitors to the Bureau.
An excellent review of the fundamental research in the decade appears in Briggs, "The
national standards of measurements," Annual Report, Smithsonian Institute, 1940,
pp. 161—176.