FOR the past few years, the council of the British Association, in co-operation with the various sections, has selected a number of scientific topics which are of direct interest to the general public, and by means of symposia or otherwise, to which workers in the particular fields concerned have contributed, general reviews of our present knowledge and the problems still to be solved have been arranged. Among the subjects chosen for the Cambridge meeting was vibration, a phenomenon which, in this mechanical age, is in daily evidence to every one of us, and the importance of which is very great. The engineer is concerned with its results upon the structure in which it occurs, which, in an aeroplane, for example, may be disastrous, and in any event will have a deteriorating effect. The ordinary person, be he traveller in motor-car, train, ship or aeroplane, is more concerned with the discomfort (and even, maybe, injury to health), which accompanies continuous vibration. From whichever point of view it is regarded, therefore, vibration is a phenomenon which everyone desires to see eliminated or reduced to a minimum.