2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/227103New historical aspects of the classification, by Cayley and Cremona, of ruled quartic surfaces and the relation to string models and plaster models are presented. In a `modern' treatment of the classification of ruled quartic surfaces the classical one is corrected and completed. A conceptual proof is presented of a result of Rohn concerning curves in $\mathbb{P}^1\times \mathbb{P}^1$ of bi-degree $(2,2)$. The string models of Series XIII (of some ruled quartic surfaces) are based on Rohn's result.35 pages, including 3 figuresAlgebraic GeometryHistory and Overview14-03; 14J26; 01A55text