Overview: James Burke explains the relationship between hot air balloons and laughing gas, and goes on to surgery, hydraulic-water gardens, hydraulic rams, tunnelling through the Alps, the Orient Express, nitroglycerin, heart attacks and headaches, aspirin, carbolic acid, disinfectants, Maybach-Gottlieb Daimler-Mercedes, carburetors, helicopters, typewriters, punch cards, and IBM.