The interpretation of writings is for the court, where they are are unambiguous, or where they are ambiguous in their terms and the ambiguity can be resolved by reference to other parts of the writing or uncontroverted circumstances; but where the terms of the writing are ambiguous, and the intention of the parties cannot be ascertained without resorting to extrinsic facts which are controverted or unconceded, intention is a question of fact for the jury. Big Four R. R. Co. v. Clark (Mo App. '09), 123 S. W. 95. See sec. 926.