The original concept of the differential analyzer can be traced back to William Thomson (later Lord Kelvin) who first published the idea in 1876 (Thomson (1876C)).  However, it was not until the invention of the mechanical torque amplifier by Nieman in 1927 (Neiman (1927)) that the machine became practical.  The first working differential analyzer was built by Vannevar Bush at MIT, and completed in 1931 (see Bush (1931)).  It was quickly copied, and in England the physicist Douglas Hartree at Manchester University and his student Arthur Porter built the first one outside of the United States using mostly standard Meccano parts.