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

CURTAILMENT BY LIMITATION OF FUNDS
tinuous recordings at varying heights of the critical frequencies of the ionized
layers responsible for reflecting radio waves back to earth.
Not a single surface, as originally believed, the ionosphere phe-
nomenon apparently consisted of a series of layers, each affecting differently
the distance obtained in radio transmission at various frequencies, at dif-
ferent times of day, different seasons, and even in different years. From "the
most complete body of data in existence on this subject," the Bureau reported
in 1934, the radio section began the first of its deductions about the roles
played in long-distance transmission by reflection and refraction and the rela-
tive effects of ultraviolet light, electrons, and heavy ions. The amassed data
on sudden fadeouts in long-distance transmission, obtained through coopera-
tive research, led in 1935 to Dellinger's confirmation of their source in sudden
eruptions on the sun, a phenomenon subsequently known as "the Dellinger
effect." 153
By 1937 the data at the Bureau made it possible to inaugurate a serv-
ice of monthly predictions of ionospheric and radio conditions. For the
first time Government long-distance stations and commercial air services were
provided with information on the selection of radio frequencies for transmis-
sion over specified distances at various times of day and year, alternative
means of radio communication when sun disturbances interfered with normal
communications, and other vital transmission information.154
One investigation in the field of applied radio in the 1930's—long
before the advent of CONELRAD or EBS (Emergency Broadcast System)—
struck a faintly ominous note, when the Federal Bureau of Investigation
requested the Bureau to make experiments to see whether voice broadcasting
NBS Annual Report 1934, p. 54; Dellinger notes in Science, 82, 351 and 548 (1935);
NBS Annual Report 1936, p. 61; RP1001, "Characteristics of the ionosphere * *
(Gilliland, Smith, and Reymer, 1937); RP1O61, "Sudden disturbances of the ionosphere"
(Dellinger, 1937).
154 The service was announced in LC499, "The weekly radio broadcast of the NBS on
the ionosphere and radio transmission conditions" (1937). LC565, "Standard fre-
quencies and other services broadcast by NBS" (1939), said the Bureau's ionospheric
reports would offer information on vertical-incidence critical frequencies, heights of the
ionospheric layers, maximum usable frequencies for radio transmission, and information
on ionospheric disturbances, thereby permitting a choice to be made in selecting optimum
frequencies for long-distance transmission.
LC614, "Radio transmission and the ionosphere" (1940), was a 22-page description of
the new ionosphere observation, reporting, and predicting service of the Bureau, analo-
gous to the Federal weather reporting service.
LC615, "Radio distance ranges" (1940), provided the first detailed data for long-distance
radio stations on ionospheric heights and ionization density of ionosphere layers, and
determination and control of optimum conditions for long-distance radio for the coming
year. This circular was superseded by LC658 (1941), with ranges for the summer of
1941 and winter of 1941—42. It was withdrawn on Jan. 2, 1942, as classified information.
The series was resumed after the war.
351