Preface to North paper

This classic report, written in 1943 by Dwight O. North, appears here for the first time in a publication readily available to the engineering profession, although it was issued as a militarysecurity- classified report during World War II (RCA Laboratories Report PTR-6C, dated June 25, 1943). It is reprinted here because of its historical importance and because it is still a basic but otherwise unavailable reference of great value in current research.