The early work of Froude. Relation of skin-friction to resistance arising from other causes. The Langley fallacy. The Reynolds Number and the condition of laminar flow: expressed graphically. Resistance as a functionl of velocity. Ichthyoid or streamline bodies: exemplifield in the Graf Zeppelin airship, etc.

We have published elsewhere a considerable amount of work on the development of the cathode ray engine indicator and, while most of the pressure elements and circuits which have been developed are perfectly satisfactory on normal petrol and Diesel engines, it has been impossible up to the present time to obtain a really satisfactory pressure-time card on the high duty boosted aircraft engine, the main difficulty being due to the super position of mechanical vibration on the pressure-time diagram. A satisfactory knock indicator has, however, been produced and a few of the results are here discussed, in the hope that they may be of general interest.