By Emily Sohn

It all started with horses. In paintings up through the 19th century, running animals looked like levitated hobbyhorses: front legs reaching forward, hind legs stretching back. But horse-racing enthusiasts had long debated whether a galloping horse ever had all four hoofs off the ground at the same time, since no one's eyes were quick enough to catch the moment.

To settle the debate, California Gov. Leland Stanford–a horse fancier himself–hired photographer Eadweard Muybridge in 1872 to capture the sequence on film. In 12 pictures taken in the space of less than half a second using 12 cameras hooked to wire triggers, Muybridge proved in 1878 that, yes, a galloping horse goes completely airborne. His photo series–which also showed the animal's legs tucked underneath its body, not splayed as everyone had assumed–appeared in the science journals Nature, Scientific American, and newspapers around the globe.

"The world of motion had been as invisible as the planets before the telescope and microbes before the microscope," says cultural historian Rebecca Solnit, author of a forthcoming book about Muybridge. "Muybridge shifted the nature of photography. Suddenly, one could see far more than the eye could see." His sequences of animals and people in motion inspired some famous works of art–including Edgar Degas's racehorse paintings and Marcel Duchamp's Nude Descending a Staircase. Other artists, such as French painter Jean Louis Ernest Meissonier, were less pleased. "Meissonier was really upset and horrified," Solnit says. "He thought he had been doing the most accurate representation of horses he could." The artist later painted new versions of many of his famous pieces to make them more precise, while many realist painters began anxiously asking themselves, as Solnit puts it, "Is truth what we see or what the camera sees?"

At the same time that Muybridge was working in California, Etienne Jules Marey, a French doctor, was also working on the horse question. After seeing Muybridge's sequences, Marey invented a camera that could capture each phase of movement in a single image. (He later invented the first motion picture projector.) Scientific applications followed quickly. Trainers and coaches designed regimens to increase the efficiency of horses and human athletes. Doctors created better prosthetic limbs. Marey even performed bird experiments that inspired the Wright brothers in inventing airplanes. Soon, stop-action technology improved, too. In the 1930s, MIT engineer Harold Edgerton invented the stroboscopic flash, enabling him to freeze, in one instance, a bullet piercing an apple at 2,953 feet per second, fantastically merging art and science.