Has been requested by Gideon Mantell to write JH a letter of introduction for a Lieut. H. I. Thomas, a friend of Davies Gilbert. Thomas wishes to be the bearer of any letter or parcel CL may have. Believes that a copy of the President's speech he sent may be lost in the post. Thinks that JH's theory of subterranean isothermal lines interesting. Dined with the Somervilles last Sunday.

Charles Babbage will publish JH's volcanic theory in Ninth Bridgewater Treatise, together with JH's letter to R. I. Murchison. William Whewell read both at Geological Society. Babbage wants to compare JH's theory with passage from Bishop [Samuel] Butler. Whewell's notion of new species. Charles Darwin's new theory of coral islands is forcing CL to give up CL's volcanic crater theory. [Letter continues 28 May.] Sends copy of Babbage's Treatise with quotes from JH. News of Charles Wheatstone's submarine telegraph and David Brewster's proof that diamond is of vegetable origin.