During the course of certain experiments conducted at the National Physical Laboratory in 1919, a number of observations were made of the normal pressure at points on the surface of a prolate spheroid of length/diameter ratio 4. The results were compared with the corresponding pressures, calculated by purely theoretical methods, on a similar body in rectilinear motion in an ideal fluid. The comparison showed that agreement between theory and experiment was remarkably good for three-quarters the length of the model, even when the axis of the model was inclined to the direction of motion. The closeness of the agreement suggested that a more extensive investigation would be likely to lead to very interesting results. It was therefore decided to conduct a comprehensive series of experiments with a view to obtaining a more complete comparison. The scope of the investigation was widened to cover not only rectilinear motion which is reproduced in wind-tunnel experiments, but to include purely rotational motion (spin about a minor axis) and also motion in a circle. The whirling arm at the Laboratory provided the necessary means for reproducing this motion in the experimental part of the work.