De Marcus: In a discussion of the formation of the solar system’s giant planets it seems necessary, even if somewhat tedious, to define our terms. Strictly this would mean some attempt to outline the past physical steps which led these bodies to their present condition. However, it seems possible that some at least of these bodies may not yet be quite through with their formation in the more general and presumably more meaningful sense that changes may still be ahead in which such basic parameters as mean density etc. may be appreciably different than the current values. I do not mean anything here as trivial as improved measures of radii which recently appreciably altered the number we refer to as the mean density of Neptune. Rather as an example of what I mean (but without asserting anything about the probability that the example is true) it could be that Saturn has much more helium than the current models indicate, in which case at some time in future his mean density might become ≈2.0 gm/cm3 or more instead of the present value of 0.7 gm/cm3. Consequently I first like to address myself to observational evidence which might suggest that such changes could happen.