Many of our most important modern inventions have been forestalled by the Chinese, for whom we should have the greater regard in that they are not Christians. Gunpowder, False Money, the art of Printing, Diplomacy, Propaganda, Prison Fortunes, Taximeters and the Strike--all these are of the extreme Orient. But what have I to do with all these? It is of the Mariner's Compass that I sing--which also was first spotted by the Chink. Now of the various forms of Mariner's Compass there is one with which some few of my readers may be acquainted. It is used in certain scientific experiments which have nothing to do with pointing to the North, but with the measurement of delicate electrical hints. The needle swings on a jewelled pivot, very nicely balanced, encased in a small round box about an inch across, covered in with glass so that no dust can affect the very sensitive affair; and at the side there is a little stud on a spring which you press with your finger when you want to fix and register the pointing of the needle. So long as you press the stud the needle stands firm. When you release the stud the needle trembles again. All very interesting. But what of it? Wait a moment. Retain this clearly in your mind, and I will proceed to the second point. It has been remarked by the less stupid of psychologists--and that is not saying much--that cunning and intelligence are not often combined. Conversely, as Dr. Nancy Neerly shrewdly remarked, when her assistant at the Hospital for Nervous Diseases, gonophed her microscope, extreme incompetence is often accompanied by cunning. Nothing is more cunning than your half-wit. Getting that principle firmly into your head, you will appreciate that when Professor de Bohun slunk out in the evening after his cousin's departure for town, into the neighbouring suburban villas of Bakeham (which, for one thing, fringed the Park--the de Bohuns had long ago screened it by a dense row of quickly-growing timber--and for another, provided the Home Secretary with a considerable part of his insufficient income) his action was not unconnected with that upon which his mind had been exercised for now nearly twenty-four hours. He sought a policeman, and said with a sudden squeak which made that high official jump: "Oh! Can you tell me if anyone round here sells scientific instruments? Optical instruments? Electrical instruments? ... Instruments?" "Wot?" said the policeman. "Let us say ... ah, for instance," went on the squeaky voice, "clinometers.... Shall we say Clinometers? Clinometers? ... Yes! Clinometers!" "Pass along!" said the policeman. "Pass along!" And there was that in his eye of a man who hesitates between a verdict of lunacy and arrest for leg-pull. "But, Constable ..." pleaded the unfortunate cadet of an ancient house.