Of late years a great deal of experimental work has been carried out with the object of determining the effect upon various metals of a load applied and removed many times in quick succession. The chief object of such researches is to determine the maximum stress which can be applied and removed indefinitely without causing fracture of the piece. Little attention has been given to any change in the structure of the metal, except in cases where there has been well-marked permanent distortion. The writer accordingly undertook some simple preliminary experiments in order to ascertain the effect upon the structure of a few alloys of numerous small blows, each of insufficient force to cause a permanent deformation of the specimens.