McCormick, T. Mitchison, U. Alon, S. Shieber, E. Lander, R. Nagpal, J. Fruchter, J. Guldi, J. Cauz, C. Cole, P. Bordalo, N. Christakis, C. Rosenberg, M. Liberman, J. Sheidlower, B. Zimmer, R. Darnton, and A. Spector for discussions; to C- M. Hetrea and K. Sen for assistance with Encyclopaedia Britannica's data