THE structure of water jets was first investigated by M. Savart, who in 1833 published a series of beautiful papers in the Annales de Chimie et de Physique. Since then it has received the attention of many experimenters, notably M. Plateau and Prof. Magnus, while of later years our knowledge of the subject has been much added to by the observations and mathematical researches of Lord Rayleigh. The older experimenters had to content themselves with observing the jet through a revolving disc with radial slots, but by means of an electric spark and rapid plates we can now secure photographs of the jet at any desired instant. The eye shows us that a jet of water consists of two parts, (1) a clear column, and (2) a troubled portion. The spark reveals to us that the troubled portion, though apparently continuous, is really a succession of drops, which move too rapidly for the eye to perceive them as such while under continuous illumination.