The origin of this memoir was a letter from Michael Polanyi (M. P.) to the present writer (P. H. P.) about their researches in the mid-1940s into the mechanism of what are now called cationic polymerizations, at the University of Manchester (England). M. P. analyzes his tactics and the mistakes made in directing this research.When the Manchester-trained researchers made little progress with what was a very recalcitrant problem, M. P. thinking that scientists from a different background might be more sucessful, got P. H. P., from Cambridge, to work with an Oxford-trained chemist. They recognized that the likely cause of the irreproducibility of these polymerizations was the apparatus used which permitted access of atmospheric moisture to the reaction mixtures containing the moisture-sensitive catalytic metal halides. Because the only method for following the very fast polymerizations was by monitoring the accompanying temperature rise, and the reactions had to be done below ambient temperature, the reaction vessel needed to be adiabatic, that is a Dewar (Thermos) flask; hence the problem of how to cool its contents. The solution was P. H. P.'s invention of the pseudo-Dewar vessel, the Dewar space of which, instead of being evacuated permanently, could be filled with air or evacuated. This device permitted the reaction mixture to be made up and cooled, and the reactions to be started without contact with the atmosphere. Thus it was found that isobutene polymerizations, which had stopped unaccountably, could be restarted by water vapor. P. H. P. termed water a "co-catalyst". The consequent "Manchester" theory recognized the monohydrate of TiCl4 as a protonic acid and saw the initiation as due to the protonation of the monomer, with the formation of a tert-carbenium ion, and these ions, formed repetitively, became the propagating species.The Manchester theory was rapidly accepted because it could also explain observations on other related reactions. The involvement of ions established a link with nonaqueous electrochemistry. (C) 2004 Wiley Periodicals, Inc.