Copy letter from Robert William Frederick Harrison, Assistant Secretary of the Royal Society; to Thomas Bon Dapray Esquire; The Christiana Apt. 21, 1829 California Street, Washington Informs Mr. Thomas Bon Dapray that he is not aware of an invention called 'The Searchlight', however, that the description given corresponds with 'Thermophones', an invention laid out in a paper by M. De Lange. Notes that an abstract of this paper was published in the 'Proceedings' and can be found in volume 92 (A). 13 February 1919