Leland Stanford had a large farm at which he bred, trained and raced both Standardbreds, used for trotting races in which a driver rides in a sulky while driving the horse; and Thoroughbreds, ridden by jockeys and raced at a gallop. He was interested in improving the performance of his horses of both types and in the scientific questions of their gait action.
During July 1877, the photographer Muybridge tried to settle Stanford's question with a series of progressively clearer, single photographs of Stanford's trotter, Occident, at a racing-speed gait at the Union Park Racetrack in Sacramento, California. He captured the horse in a photograph with all four feet off the ground. One of the prints was sent to the local California press, but because they found that the film negative was retouched, the press dismissed it. As negative retouching was an acceptable and common practice at the time, the photograph won Muybridge an award at the Twelfth San Francisco Industrial Exhibition. Lantern slides of the trotting horse photographs survive.
The following year, Stanford financed Muybridge's next project: to use multiple cameras to photograph a Thoroughbred at a gallop at Stanford's farm in Palo Alto on June 15, 1878, in the presence of the press. Muybridge photographed the businessman's Kentucky-bred mare named Sallie Gardner running.
He had arranged the cameras along a track parallel to the horse's path. Muybridge used 24 cameras which were 27 inches (69 cm) apart. The shutters were controlled by trip wires triggered by the horse's legs. The photographs were taken in succession one twenty-fifth of a second apart, with the shutter speeds calculated to be less than 1/2000 s. The jockey Domm set the mare to travel at a speed of 1:40, which meant that she was galloping at a mile per 1 minute and 40 seconds, equivalent to 36 miles per hour (58 km/h).
The stop-action photographs showed the mare lifted all four legs off the ground at certain points during the gallop. Run together, the photographs produced the effect of the horse in motion, or a film. Muybridge produced his prints onsite; when the press noticed the broken straps on Sallie's saddle in the prints, they became convinced of the prints' authenticity. Scientific American was among the publications that carried reports of Muybridge's groundbreaking 1878 work. While there have been rumors that Stanford had a large bet riding on the outcome of the study, the historian Phillip Prodger has said, "I personally believe that the story of the bet is apocryphal. There are really no primary accounts of this bet ever having taken place. Everything is hearsay and secondhand information."
In 1880, Muybridge first projected moving images on a screen when he gave a presentation at the California School of Fine Arts; this was the earliest known motion picture exhibition. He later met with Thomas Edison, who had recently invented the phonograph. Edison went on to invent the kinetoscope, the precursor of the movie camera.
The relationship between Muybridge and Stanford became turbulent in 1882. Stanford commissioned the book The Horse in Motion: as Shown by Instantaneous Photography, written by his friend and horseman J. D. B. Stillman; it was published by Osgood and Company. The book claimed to feature instantaneous photography, but showed 100 illustrations based on Muybridge's photographs taken of Stanford's mare Sallie. Muybridge was not credited in the book except noted as a Stanford employee and in a technical appendix based on an account he had written. As a result, the Britain's Royal Society of Arts, which earlier had offered to finance further photographic studies by Muybridge of animal movement, withdrew the funding. His suit against Stanford to gain credit was dismissed out of court.
Muybridge soon gained support for two years of studies under the auspices of the University of Pennsylvania. The university published his current and previous work as an extensive portfolio of 780 collotype plates, under the title Animal Locomotion: An Electro-photographic Investigation of Consecutive Phases of Animal Movements, 1872–1885. The collotype plates measured 19 by 24 inches, each were contained in 36 by 36-inch frames; the total number of images were approximately 20,000. The published plates included 514 of men and women in motion, 27 plates of abnormal male and female movement, 16 of children, 5 plates of adult male hand movement, and 221 with animal subjects.
The "Sallie Gardner" experiment was the subject of a Google doodle on April 9, 2012 (on the 182nd anniversary of Muybridge's birthday).