Thomas Hawksley lecture, Heat engines** first Thomas Hawksley lecture, by E. B. Ellington, proc. I.Mech.E., 1913, page 1215. Second lecture, by W. B. Bryan, 1914, page 811. Third lecture, by Dugald Clerk, D.Sc., F.R.S., 1915, page 591. Fourth lecture, by Harry E. Jones, 1916, page 631.