Recent Technical Developments: A German Non‐Periodic Compass—Light on the Life of Aero Engines—A New Tinning Compound with Cleansing Properties—The Pioneer Instrument Company's Sun Compass

New Light Aeroplane Compass An interesting light aeroplane compass has just been introduced to this country by E. F. Stephen, of 141, Bond Street, who will be the sole concessionaire lor this country. Known as the “ZN” compass, the German makers, “Zürn, Jackenkroll & Co., claim for it that it is a definite improvement on existing compasses in that it is non‐periodic rather than aperiodic. That is to say, by careful design it has been possible to make the value of the magnetic moment so large in proportion to the amount of inertia that only a comparatively small amount of damping is necessary to eliminate oscillation.