2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/67899We describe the relationship between complex-valued harmonic morphisms from Minkowski 4-space} and the shear-free ray congruences of mathematical physics. Then we show how a horizontally conformal submersion on a domain of Euclidean 3-space gives the boundary values at infinity of a complex-valued harmonic morphism on hyperbolic 4-space.38 pages, needs lms.sty, 3 ps figures. This is a revised and expanded version of dg-ga/9603005, and forms a supplement to the authors' book `Harmonic morphisms between Riemannian manifolds', see http://www.amsta.leeds.ac.uk/Pure/staff/wood/BWBook/BWBook.htmlDifferential Geometry53C43 (Primary); 58E20 (Secondary)text