Type III solar radio bursts are investigated by modelling the propagat
ion of the electron beam and the generation and subsequent propagation
of waves to the observer. Predictions from this model are compared in
detail with particle, Langmuir wave, and radio data from the ISEE-3 s
pacecraft and with other observations to clarify the roles of fundamen
tal and harmonic emission in type III radio bursts. Langmuir waves are
seen only after the arrival of the beam, in accord with the standard
theory. These waves persist after a positive beam slope is last resolv
ed, implying that sporadic positive slopes persist for some time, unre
solved but in accord with the predictions of stochastic growth theory.
Local electromagnetic emission sets in only after Langmuir waves are
seen, in accord with the standard theory, which relies on nonlinear pr
ocesses involving Langmuir waves. In the events investigated here, fun
damental radiation appears to dominate early in the event, followed an
d/or accompanied by harmonic radiation after the peak, with a long-liv
ed tail of multiply scattered fundamental or harmonic emission extendi
ng long afterwards. These results are largely independent of, but gene
rally consistent with, the conclusions of earlier works.