306 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
It will be noticed that, until this point, the existence of these 
disturbances and the measurement of their speed have been inferred 
from the interpretation of the emitted radio frequencies in terms of 
an equivalent height in the solar atmosphere. Thus, a rate of change 
of frequency is interpreted in terms of a rate of change of height, 
which is the mathematical expression of velocity. Over the past year, 
these plausible assumptions have been brilliantly confirmed in an ex- 
periment which combines both sweep frequency equipment and an 
interferometer, to give a direct measure of the translational velocity 
of these disturbances. This work, carried out in Australia by J. P. 
Wild, shows that these spectacular forms of solar radio bursts are 
definitely caused by disturbances moving outward through the solar 
atmosphere with the velocities quoted above. 
SOLAR RADIO BURSTS AND LOW-ENERGY COSMIC RAYS 
Recent observations, with scintillation and Geiger counters carried 
in satellites and balloons, have shown that the terrestrial atmosphere 
is frequently bombarded by solar protons of energies 30-300 Mev., 
which may be designated low-energy cosmic rays. The solar protons 
have been detected outside the Van Allen radiation zones, at high 
magnetic latitudes. Because of their low magnetic rigidity, these 
particles can penetrate the terrestrial atmosphere only in the vicinity 
of the magnetic poles, and in these regions they also give rise to 
ionospheric polar blackouts. 
There has been much speculation concerning the origin of the low- 
energy solar cosmic rays, and their relation to solar radio bursts and 
flares. Examination of the solar radio data recorded over the past 18 
months shows that the low-energy cosmic rays are preceded by radio 
bursts of an unusual and exciting nature. Among solar radio as- 
tronomers these are known as continuum bursts of spectral Type IV. 
This type of radiation characteristically covers several octaves of 
the radio spectrum, is generally of great intensity, and often lasts for 
many hours. It has been suggested that it originates from a synchro- 
tron mechanism (the Schwinger mechanism), in which electrons with 
relativistic velocities are trapped in orbital motion in a magnetic field. 
The onset of the synchrotron radiation is generally preceded, about 
15 minutes ahead, by a solar flare, usually of importance 3 or 3+. 
Approximately 1 hour later, solar protons commence bombarding 
the earth. This sequence of events is now quite clearly established, 
and it has already occurred five times this year. On May 11 and 12, 
1959, the integral flux of protons at the top of the atmosphere in- 
creased by a factor of approximately 1,000 over the galactic cosmic 
ray component, and the composition of the incoming beam was es- 
sentially pure hydrogen. This spectacular increase in the proton 
count was preceded by solar radio outbursts of the continuum type on 
