Viktor Trkal,Beltrami fields,and Trkalian flows

A 1919 contribution of Viktor Trkal on Beltrami fields is contextualized and shown to be of significance in fluid mechanics, time-harmonic electromagnetism and astrophysics.This paper introduces the English translation of an article by V. Trkal from 1919 — see next paper in this issue, p. 97.I gratefully acknowledge the assistance of Drs. Per Lindstrom (Bergen, Norway), Avadh B. Saxena (Los Alamos, New Mexico), Chandra S. Vikrarn (Huntsville, Alabama) and Miloslav Znojil (Prague) in locating old publications. I also thank the editors of this journal for asking me to write this introductory piece as well as for readily agreeing to publish an English translation of Trkal's paper.