On logic and mathematics; on the 4th volume of Principia, criticizing a Dr. Langford: "His remarks about the projected fourth volume of that work are also very wide of the mark. There was no difficulty whatever in formalizing geometry. Whitehead did a great deal of the preliminary work which consisted in inventing a symbolism for triadic and tetradic relations, but the first war turned him aside from the work and he decided not to complete it."