A radical shift in the velocity and volume of general mobility was a sine qua non of mass emigration. The pre-existing shape of labour mobilities set the context for the emergence of mass emigration. The beginnings of mass emigration were located in the British Isles in the 1820s, but the scale of the discontinuity requires a measure of the circumstances before the change. Modern mass mobility erupted in the western world in the early nineteenth century, especially in Victorian times. The case of Alexander Somerville in Scotland provides a standard pattern for mobility in the transitional age. English historians have long identified an array of categories of mobility in the pre-modern population, some long-distance, some seasonal, some local and circulatory. A composite picture has emerged which emphasises the essential fluidity of the population before industrialisation, of people in localised motion and perhaps increasingly so.