Letter [Bertram] Hopkinson, Engineering Laboratory, Cambridge, to the Assistant Secretary of the Royal Society, Burlington House 'Dear Sir, In reply to your letter enclosing a communication from the "Gas World", I think it would be satisfactory to send them a copy of the abstract of my paper. Before any abstract is sent out for publication, however, I should like to see a proof as I want to add a note with reference to some remarks which Professor Callendar made at the discussion of the paper. Yours truly, B Hopkinson'. 12 February 1906