MESSRS. ROLLS ROYCE have introduced a new-system of water cooling under pressure on their “Merlin IV” engine. This is similar to the usual atmospheric one, but is closed and provided with loaded valves, so that the boiling point of the water under pressure is raised. The many recent developments in metallurgy and lubricating oils have made it possible for the internal combustion engine to function at higher temperatures, and thus to increase thermal efficiency, in addition to the obvious advantage of using smaller radiators with both less drag and weight. The more general method up to the present of maintaining the engine at the higher temperature permissible has been to use liquids with higher boiling points. Ethylene glycol is the most generally used in Great Britain, but this has objections in its corrosive effect upon parts of the cooling system, especially the inevitable joints, if a substance such as a rubber or leather compound is used. Extra cost, and the necessity of carrying a supply of the special liquid, are also points against such preparations. The new radiator and cooling system fittings may need to be somewhat more robust for dealing with pressure, but this is not altogether a disadvantage in that the more solid construction will add to its reliability. Weakness due to flimsy construction has often been typical of the older water cooling systems. It is reported that these engines with their new cooling will be fitted to the Armstrong AVhit-worth “Whitley” the new R.A.F. bomber, now coming into production.