The migratory movement is at once perpetual, partial, and universal. It never ceases, it affects every people, but at a given moment it sets in motion only a small number of each population; hence the illusion of immobility. In fact, there is never a moment of immobility for any people, because no migration remains isolated
[archiveorg EuropeOnTheMove width=560 height=384 frameborder=0 webkitallowfullscreen=true mozallowfullscreen=true]
https://archive.org/download/EuropeOnTheMove/Europe-On-The-Move.pdf