On January 7th, 1894, William Kennedy Dickson (a Scottish inventor who invented a prototype of the motion picture camera) received a patent for motion picture film. Dickson, who worked for a time with Thomas Edison in his film studio, is also responsible for creating the short film Dickson Greeting, considered by some to be the first film shown to an American audience (produced circa 1891).
If you look at the late 19th century films that have survived to the present day, you’ll notice that they’re all incredibly short by modern standards, and why is this? The reason the earliest films are so short is because when these inventors created the process of running film through a motion picture camera, the material used for film was incredibly flammable and those first cameras made it relatively easy for the film to overheat and catch fire if it ran too long. So, they adjusted the length of film to a certain length that they knew could run safely, and as the technology improved, the films grew longer in length.