Ruled quartic surfaces, models and classification

New historical aspects of the classification 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. The string models of Series XIII of some ruled quartic surfaces are based on a result of Rohn concerning curves in P1 × P1 of bi-degree (2, 2). This is given here a conceptional proof