In 1872 former governor of California and railroad tycoon Leland Stanford, founder of Stanford University, hired the English photographer Eadweard Muybridge to settle a debate whether, during its gait, all four of a horse's hooves are simultaneously off the ground. This challenged Muybridge to look for a way to capture the sequence of movement. In 1878, after six years of work on the project, Muybridge succeeded. He arranged 12 trip-wire cameras along a racetrack in the path of a galloping horse. The resulting photo sequence proved that there is a point when no hooves touch the ground and set the stage for the first motion pictures.
"In 1872, Muybridge settled Stanford's question with a single photographic negative showing his Standardbred trotting horse Occident airborne at the trot. This negative was lost, but the image survives through woodcuts made at the time (the technology for printed reproductions of photographs was still being developed). He later did additional studies, as well as improving his camera for quicker shutter speed and faster film emulsions. By 1878, spurred on by Stanford to expand the experiments, Muybridge had successfully photographed a horse at a trot; lantern slides have survived of this later work. . . .
"Stanford also wanted a study of the horse at a gallop. Muybridge planned to take a series of photos on 15 June 1878 at Stanford's Palo Alto Stock Farm. He placed numerous large glass-plate cameras in a line along the edge of the track; the shutter of each was triggered by a thread as the horse passed (in later studies he used a clockwork device to set off the shutters and capture the images). The path was lined with cloth sheets to reflect as much light as possible. He copied the images in the form of silhouettes onto a disc to be viewed in a machine he had invented, which he called a zoopraxiscope. This device was later regarded as an early movie projector, and the process as an intermediate stage toward motion pictures or cinematography.
"The study is called Sallie Gardner at a Gallop or The Horse in Motion; it shows images of the horse with all feet off the ground. This did not take place when the horse's legs were extended to the front and back, as imagined by contemporary illustrators, but when its legs were collected beneath its body as it switched from "pulling" with the front legs to "pushing" with the back legs" (Wikipedia article on Eadweard Muybridge, accessed 10-24-2013).