LONDON. Royal Society, June 30.—A. V. Hill, K. Furusawa, and J. L. Parkinson: The dynamics of ‘sprint’ running. By an application of the theory of dimensions it is shown that the speed of an animal, such as is limited by the inertial stresses to which the structures are subjected during movement. The ‘viscosity’ of the muscles is the chief factor. For experimental work it is necessary to employ maximal contractions. The case of submaximal contractions is theoretically discussed. A runner exerting maximal effort propels himself with constant force. The ‘constants’ of a given runner can be determined with very fair accuracy, and the work done, in running, against viscosity and resistance of the muscles can also be determined.