Interstellar Travel

James Blish conceptualizes requirements or adjuncts of interstellar travel:

the spindizzy or the Haertel overdrive and its successors;

the ultrawave/ultraphone, the Dirac transmitter, the CirCon radio;

the germanium-based Oc dollar, the Traitors's Guild;

the anti-agathics;

pantropy.

Cities In Flight has the spindizzy, the ultraphone, the Dirac transmitter, the Oc dollar and the anti-agathics;

The Seedling Stars has an unspecified overdrive, the ultraphone, the Oc dollar and pantropy;

The Quincunx Of Time has the Haertel overdrive, the ultraphone and the newly invented Dirac transmitter;

"A Style in Treason" has the Imaginary Drive, the ultraphone and the Traitors' Guild (an interstellar bourse);

Midsummer Century has ultrawave and Dirac;

A Case Of Conscience has the Haertel overdrive and the newly invented CirCon (circum-continuum) radio;

Narratives diverge. Anti-agathics entailed the possibility of some characters living until the end of the universe which, however, for fictional convenience, was brought unexpectedly close to the present whereas pantropy entailed the possibility of Adapted Men inhabiting the entire galaxy millennia hence.

Although the Dirac transmitter was introduced in the first written Okie (Cities In Flight) story, the propagation of Dirac pulses in a four-dimensional continuum had consequences that did not fit into that series so the idea was developed more fully elsewhere. The stories of the discoveries of the spindizzy and of anti-agathics were incorporated into Volume I of Cities In Flight whereas the invention of the Dirac transmitter is described in The Quincunx Of Time.