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

GEORGE KIMBALL BURGESS 245
and often of more immediate interest to science than to industry. Such was
the work of Vinal and his associates from 1912 to 1916 which resulted in
more precise knowledge of the limitations in accuracy of the silver voltam-.
eter (the reference standard for defining the International Ampere), requisite
to the later absolute determination of the ampere.69 A fine achievement also
was Heyl's redetermination of the Newtonian constant of gravitation (G) and
later of the value at Washington of the local acceleration of gray.
ity (g), completing as it did a "true weighing of the earth." 70 Signifi-
cant too were Buckingham and Dellinger's work on a method of computing
the constant of Planck's equation for the radiation of a black body,71 Gibson
and Tyndall's determination of visibility factors of radiant energy,72 and
Coblentz's new standards of thermal radiation, also involving Planck's equa-
tion, the latter published in a 75-page report on which Coblentz worked from
1909 to 1912. The values of those standards remain unchallenged to the
present day.73
Although astronomers at the time, as Coblentz, said, would have
seriously questioned the possibility of detecting "the heat of a candle 52
miles away," the series of highly sensitive radiometers which he devised for
his research made possible new measurements of the heat of stars and planets.
His instruments were destined to extend the fields of spectroscopy and colorim-
etry and find application in the biological and agricultural sciences.74
In one investigation Burgess joined Coblentz, when both became inter-
ested in the international research going on in the high-temperature optical-
pyrometer scale and the laws of radiation upon which to base such a scale.
68 S218 (Vinal and S. J. Bates, 1914); S285 (Vinal and Rosa, 1916).
'° The work spanned almost 20 years. See letter, SWS to Superintendent, C. & G. S.,
Feb. 20, 1917 (NBS Box 2, AG); NBS Annual Report 1923, p. 200; Annual Report
1927, p. 6; RP256 (Heyl, 1930); RP946, "The value of gravity at Washington" (Heyl
and Cook, 1936).
S162 (1911). Other work at the Bureau involving Planck's constant was reported
in S259 (Foote, 1916), S287 (Dellinger, 1917), S304 (Roeser, 1918), and Foote and
Mohler, J. Opt. Soc. Am. 2, 96 (1919).
Planck had modified the earlier Wien equation for black-body radiation to better fit the
experimental data of Rubens, Coblentz and others. It was his search for a theoretical
explanation of this equation which led to his famous postulate of the energy quantum,
hv, which laid the foundation for his quantum theory. His equation involving the con-
stant c2 gives the spectral energy distribution of the heat radiation emitted from a
so-called black body at any temperature. Among many applications, the constant can
be used to predict the light output of incandescent lamps, cooling time of molten steel,
heat dissipation of a nuclear reactor, the energy radiated from the sun, or the temperature
of the stars.
'2S475 (1923).
S204 (1913) and S227 (1914); Coblentz and Stair, "The present status of the stand-
ards of thermal radiation maintained by the Bureau of Standards" (RP578, 1933).
Coblentz, From the Life of a Researcher, pp. 14.8, 154, 168—173.