The "great chain of being" that had served as a metaphor for the eighteenth century, whether in Lockean chains of association or in the chain-stitch of the later sewing machines, carried over incongruously into the nineteenth-century revolutionary hypothesis of the "missing link." Just as NASA scientists are still locked up in the world of Newtonian visual space, so physicists are still loyal to the stop-response of literary mechanism when they speak of "chain reactions."