ONE of the most ancient, as it is one of the most intellectual, games played by mankind, chess is by now almost an exact science, and it can be discussed in an almost scientific vein. The very large number of listeners who are also chess enthusiasts will welcome this evening's talk in which Mr. Brian Harley , Chess Editor of The Observer, will discuss that popular opening move, the Queen's Gambit Declined. Two diagrams illustrative of this talk will be found on pages 370 and 371.