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

SOME FUNDAMENTAL WORK ON STANDARDS 337
Meeting in Paris the year after the Conference of 1927, an interna-
tional advisory committee on electricity proposed the establishment of elec-
trical units based on the fundamental units of mechanical energy, the
centigrade-gram-second system, rather than the practical but arbitrary units
then in use. To this end the Bureau in 1934 published Dr. Curtis's absolute
determination of the ampere and its relation to the accepted international
unit, and in 1936 his absolute determination of the ohm.113 Moreover, the
new apparatus constructed for these determinations made it possible to main-
tain and transfer working standards of the units to other laboratories for
purposes of intercomparison.
Anticipating a rapid conclusion to the work, the international advis-
ory committee predicted general agreement on the new electrical values
within 2 years and their formal adoption by January 1940. But by 1939,
as the laboratories in Europe continued to delay reporting their work, the
Bureau had constructed still better apparatus than that used in its original
determinations and was working toward even greater precision in its meas-
urements. The adjustment of discrepancies and final agreement with the
laboratories abroad were suspended until after the war.114
Also deferred by the war was final adoption of new and practical
photometric units, based on a scale of color temperatures developed during
the 1930's.1'5 While the photometric measurements involved psychological
factors and could not be put on an absolute basis, the national laboratories
subsequently reached agreement on a single, practical, worldwide system of
units, in place of the diverse units and standards then prevailing.
The new photometric units were made possible by the adoption of a
standard visibility curve, based mainly on earlier work of Coblentz, Emerson,
Gibson, and Tyndall,"6 and by the realization of the Waidner.Burgess abso-
lute standard of light, first proposed in 1908 and achieved experimentally for
the first time in 193L"7 Together with absolute units of electricity, interna-
tional adoption of the photometric units was accomplished at last in 1948.
113 RP685 (H. L. Curtis and R. W. Curtis, 1934); RP857 (Curtis, Moon, and Sparks,
1936).
114
NBS Annual Report 1936, pp. 58—60; Annual Report 1939, pp. 49—50. In RP1606
(1944), Curtis reviewed the experimental work on the absolute units and in C459 (1947)
announced their international adoption, along with the photometric units, effective Jan. 1,
1948. The former electrical units, last adjusted in 1912, were then 50 years old.
The reproducible color temperature scale, consistent with the International Temperature
Scale, was reported by Wensel, Judd, and Roeser in RP677 (1934).
and S305 (Coblentz and Emerson, 1918); S475 (Gibson and Tyndall, 1923).
117 See ch. III, pp. 111—112; NBS Annual Report 1930, p. 10; "A primary standard of
light," Science, 72, 109 (1930) ; RP325 (Wensel, Roeser, Barbrow, and Caldwell, 1931);
RP699, "Determination of photometric standards * * * (ibid., 1934); NBS Annual
Report 1937, p. 64; Annual Report 1938, pp. 69—70.