From C. W . Siemens [Charles William Siemens, industrialist, 1823-1883], thanks Joule for his paper on the air engine, and suggests could have used his work on the subject; his own calculations show the effect of the "expansive Air Engine" are similar to Joule's. Refers to a forty horsepower engine he has made, worked by superheated steam, which gives "very satisfactory results", and has identified "some curious phenomena" which would like assistance with.
Dated at: 7 Adelphi Terrace, London.