Aerodynamics. — Some problems of the motion of interstellar gas clouds. I

Abstract

The following considerations have arisen from discussions with prof. dr. J. H. Oort at Leiden, who suggested most of the problems and to whose interest and advice I am greatly indebted in preparing these notes¹). They must be taken, nevertheless, as a very preliminary attempt towards the application of aerodynamics in analysing some of the intricate riddles that are presented by the results of astronomical observations on the interstellar material within our Galaxy. Apart from the difficulties inherent in aerodynamics itself or arising when it is applied to matter in a state of such extreme dilution, astronomical observation, notwithstanding the powerful methods of photography and spectroscopy and the beauty of all what has already been revealed, still gives us only very scanty information about the structure and the motion of the cosmic clouds. In attempting to make a few calculations many guesses must be introduced, as otherwise it is impossible to construct simple pictures which can serve as starting points for a provisional theory. The reader therefore must take for granted that the cases treated in the following pages are no more than examples, which it is hoped may elucidate a few features, and perhaps point to a way for further work.