For Tuesday September 1, 2009J. Bradford DeLongProfessor of Economics, U.C. BerkeleyResearch Associate, NBERThis Draft: July 28, 2009Take the WABAC machine back in time to 1870. Why 1870? One reason is that we have to start sometime—an economic history of the twentieth century does not properly begin with East African Plains Apes evolving language back on the veldt. More important is that the years around 1870 are a sea change, because they do contain inflection points in three important aspects of material life: communication (with implications for finance and organization); transportation (with implications not just for