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By the beginning of the 1970s the spiral subject was in considerable disarray. The still popular QSSS hypothesis of Lin and Shu, along with their illustrative semi-empirical theory, was confronted with serious difficulties. Lin and his associates were put clearly on the defensive over their tightly wrapped (quasi)-steady modes on two principal fronts: from the radial propagation at the group velocity that would tend to wind them almost at the material rate, and from the tendencies of galaxy disks toward a strong global instability that appeared likely to overwhelm them. Of course, one might claim that all such threats were just imaginary and temporary, and only of academic interest, on the ground that nature itself had overcome them (as say for the case of the bar-making instability of stellar disks, the rescue from which was actively sought in the 1970s in a massive inert halo that in fact was not needed). One might also be confident that the QSSS hypothesis must be correct, as illuminated by the everlasting truth of Hubble's classification of the galactic morphologies. One might even take pride in the historical fact that an interesting and very promising concept developed, although not connected to the wave steadiness, on spiral shocks in interstellar gas and their induced star formation. But such a heuristic approach did not stimulate very strong progress in understanding dynamical principles of the spiral phenomenon; moreover, it often misled, and a rich irony was already that the supposed QSSS favorites M51 and M81 (Lin held originally that a large majority of the galaxies - 70% - "are normal spirals like the whirlpool" (Lin 1966a, p.877)) turned out most probably not to be quasi-steady at all. A further irony was the continuing failure of Lin and Shu to account the trailing character of their `modes', while that was already grasped by their direct `deductive' opponents. But the greatest irony lay in the fact that the concept later known as swing amplification, worked out by the mid-1960s, was originally denigrated by Lin's camp as relating exclusively to `material arms', whereas it turned out in the end to be of vital importance to this entire spiral enterprise including the variants of chaotic ragged patterns, tidal transient grand designs and growing or quasi-steady modes.

The 1970s that came promised many interesting events in the spiral arena, because - here we repeat what we said in the beginning of the paper and with it close our narrative - by that time it had become very clear to everyone that much hard work still remained to explain even the persistence, much less the dynamical origins, of the variety of spirals that we observe.


The present Papers I and II were made possible thanks entirely to the generous and responsive participants of the events described. V. Antonov, G. Contopoulos, P. Goldreich, C. Hunter, W. Julian, A. Kalnajs, C.C. Lin, P.O. Lindblad, D. Lynden-Bell, F. Shu, A. Toomre and C. Yuan provided me with important materials, memories, opinions, and also gave me, kindly and patiently, answers and comments on my endless queries. Various help also came from L. Athanassoula, G. Bertin, H. Eisenberg, A. Fridman, I. Genkin, G. Idlis, V. Korchagin, I. Korshunova, G. Kulikov, G. Kurtik, M. Maksumov, Yu. Mishurov, D. Muhamedshin, M. Orlov, L. Osipkov, V. Polyachenko, A. Rastorguev, M. Roberts, E. Ruskol, J. Sellwood, K. Semenkov, V. Sheremet, F. Tsitsin. My special thanks go to T. Agekian, V. Gorbatsky and V. Orlov for their kind invitations for me to speak at their seminars at the St. Petersburg State University, and also to E. Kolotilov and V. Komissarov for their hospitality during the period I was completing the manuscript at the Crimean station of the Sternberg State Astronomical Institute in the summer of 2003.

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