www.thelancet.com Vol 372 October 25, 2008 1457 Public-health posters are a window into the history of medicine and the politics of public health. Developed out of mid-19th-century mass media campaigns to sell products, announce performances, and propagandise in western and central Europe, they were intended to promote healthy behaviours among individuals and so strengthen the body politic. By ...

W ith a shovel excavator, its operator can effortlessly move 720 tons of earth with a single movement. On the other end of the spectrum, a VLSI fabrication plant lets designers create elaborate submicron structures. Without tools, a car factory's thousands of employees can't accomplish much; with tools, they can assemble a car in 18 effort-hours. Sometimes, tools can even subsume their operator...