Referee's report by Louis Napoleon George Filon, on a paper 'Castigliano’s principle of minimum strain-energy' by Richard Vynne Southwell Sectional Committee: Mathematics Recommended for publication in the 'Proceedings of the Royal Society of London'. Refers to work of Adhémar Jean Claude Barré de Saint-Venant, which part of the paper requires modification, as the principle has not really been proved. Provides detailed list of suggested modifications and omissions, to aid in clarity. [Published in the 'Proceedings of the Royal Society of London'] Endorsed on verso as received 19 November 1935. 17 November 1935