Ever wondered how filmmakers do all the crazy scenes and stunts without the help of special effects back in the day? Now, Reddit user Auir2blaze put together an awesome compilation of movie effects from the Silent Film era, along with a brief explanation on how each effect was achieved. If you want you can watch all of his collection at Imgur.
When Safety Last! was made, it wasn’t feasible to insert a fake background using rear projection or a green screen, so they used a trick of perspective. The set was built at the right height for Lloyd’s climb, but on the roof of a building across the street. As Lloyd climbed higher, the set was moved to taller buildings. [source]
The method for achieving this much copied shot was figured out by Fairbanks’s brother Robert, an engineer. The camera and the sail were both placed at an angle. Fairbanks’s knife was connected to a hidden pulley and counterweight. Airplane propellers were used to make the sails billow. [source]
The two halves of her face were filmed separately, using a matte shot. Basically, a piece of glass with half the frame painted black was placed in front of the camera, so only one side the film was exposed. The film was then wound back, the glass was switched for one with black on the other side. The key was to avoid having either the camera or the Moore’s face shift in position while shooting, or the effect would be ruined. [source]
A good example of the classic movie making technique of glass matte painting. Part of the background was painted on a piece of glass, which was placed in front of the camera. [source]