Paper, 'On the tension of recently formed liquid surfaces' by Lord Rayleigh [John William Strutt] Strutt writes: 'It has long been a mystery why a few liquids, such as solutions of soap and saponine, should stand so far in advance of others in regard to their capability of extension into large and tolerablys durable laminae. The subject was specially considered by Plateau in his valuable researches, but. with results which cannot be regarded as wholly satisfactory. In his view the question is one of the ratio between capillary tension and superficial viscosity. Some of the facts adduced certainly favour a connexion between the phenomena attributed to the latter property and capability of extension; but the “superficial viscosity” is not clearly defined, and itself stands in need of explanation.' Annotations in pencil and ink throughout. Subject: Fluid dynamics Received 13 February 1890. Read 6 March 1890. A version of this paper was published in volume 47 of the Proceedings of the Royal Society as 'On the tension of recently formed liquid surfaces'. 1890