The data were recorded by F.H.C. Crick and B.D. Ripley, and analysed in Ripley (1977, 1981) and Diggle (1983). They are often used as a canonical example of an `ordered' point pattern.
"ppp"representing the point pattern of cell centres. See
ppp.objectfor details of the format.
Ripley, B.D. (1977) Modelling spatial patterns (with discussion). Journal of the Royal Statistical Society, Series B 39, 172--212.
Ripley, B.D. (1981) Spatial statistics. John Wiley and Sons.