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

80 FOUNDING THE NATIONAL BUREAU OF STANDARDS (1901-10)
researches. One was a study of the silver voltameter, used in measuring
current; the other comprised two closely related 'studies, a redetermination
of the electrochemical equivalent of silver and of the absolute value of the
Clark standard cell and its rival, the Weston cell.'52
Dr. Rosa's account of the inductance and capacity section suggests
that he thought it probably one of the best and most completely equipped at
the Bureau. As section chief, with Dorsey and Grover running the research,
he had high hopes for the work it had begun. Hundreds of mica and paper
condensers had been purchased from German, English, French, and American
firms and studies made to find the best performance among 'them as standards
of capacity. Two large air condensers had been constructed as loss.free
working standards against which commercial condensers sent to the Bureau
were compared. In conjunction with new apparatus under construction,
these air condensers were to make possible absolute measurement of currents
and electrical pressures up to 1,000 volts.
With a carefully constructed absolute standard of inductance (an
electrical quantity analogous to mechanical inertia), the section planned,
"by a method never before used," a new determination of the ohm, prelimin-
ary to an extended investigation in the absolute measurement of the funda-
mental electrical units, the ohm, volt, and ampere.5'8 Establishment of the
Bureau's standard of inductance would also make possible a thorough study
of common sources of error in inductance measurements, of considerable
concern to new developments in the communications industry.
The electrical measuring instruments section, also under Rosa's fervent
eye, possessed a wonderful array of precision instruments for measuring
electric current, voltage, and power, both direct and alternating, acquired
from the best instrumentmakers at home and abroad or designed and built in
the Bureau shops. The section was prepared to test and calibrate any labo-
ratory or commercial instrument then in use. Its heavy equipment included
powerful direct.current as well as alternating.current generators and allied
equipment, and in testing direct.current instruments the section was pre-
pared to handle capacities up to 1,000 amperes and 1,000 volts. The first
high-voltage studies would begin with the installation of a giant storage
battery with a potential of several thousand volts, then under construction for
the Bureau.
The Clark cell, invented in England, had been in use since 1872. The American
Weston cell, using cadmium instead of zinc, appeared in 1893, and at the turn of the
century, because of the availability of better chemical components, was being made in
Berlin. The superiority of the Weston cell had led to its adoption as a working standard
by the PTR. In 1908, by international agreement, it displaced the Clark cell as the
standard of electromotive force.
Stratton and Rosa, "The National Bureau of Standards," Proc. AIEE, 24, 1075 (1905).