We appreciate Billings' informative commentary on the problem of the temperature structure of the solar corona. We regret that we were unaware of the article by which first suggested that a large ion-electron temperature difference might result from a combination of nonthermal heating of the ions and thermal conductivity of the electrons.
The modest aim of our article was to estimate the ion-electron temperature difference resulting from a simple model, taking into account the force equation and heat equation, but assuming an arbitrary form for the energy input into the ion and electron components. The final statement of our article was: "... it is essential to investigate in more detail the heating of the solar corona, to determine in particular the allocation of energy between the electron gas and the proton gas."
Since we considered a very limited range of the possible cases allowed by our basic hypothesis, our calculations can show only what is possible; they cannot show what is not possible. For this reason, we take issue with Billings' final statement: "The large line-width temperature at greater heights remains completely unexplained by the hypothesis, of the paper by Knight et aI." (Emphasis added.) Our view is that one can conclude from our paper only that the large line-width temperature at greater heights is unexplained by the models presented in our paper. On the other hand, if the further investigation of a wider range of models shows that no such choice will explain the large line-width temperature at greater heights, then we shall agree with Billings that this observational fact contradicts the underlying hypothesis.
However, as we stressed at the end of our article, we believe it to be important at this time to try to determine the heating function rather than to make further arbitrary assumptions concerning its form.