Leland Stanford, a businessman, former governor, and race-horse owner, hired a man by the name of Eadweard James Muybridge to help him answer two basic questions:
1) Does a horse have all four feet off the ground during a trot?
2) During a gallop, does a horse have its hind legs extended to the rear and its front legs extended to the front while all four are in the air? Or, are the legs collected under its body when they are all in the air?
Solving the mysteries
To answer these questions Muybridge placed numerous large glass-plate cameras in a line along the edge of a track; the shutter of each was triggered by a thread as the horse passed. 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.
That means horses were part of the early development of movies! Very cool!
Muybridge was able to prove that a horse did have all four feet off the ground during a trot. And during the gallop, a horse is airborne when the its legs are collected under the body. You can see this clearly in the image below.