In a recent article on supercharging, various practical conditions are given which place limits on the degree of supercharging possible with aero engines. Some time ago the writer was shown the results obtained with a supercharged engine and, although the performance was very creditable up to an altitude of 12,000 feet, above this altitude there was a remarkable decrease in power, this decrease being so considerable that it could not be readily accounted for. Various modifications were made in an attempt to improve the engine's performance at the higher altitudes, but without success, and it was only after a new type of carburettor had been fitted that improved results were obtained.