Mechanical Principles (1930) by Ralph Steiner [4min selection]

 

Favorite movements:
@ 1:16 - counter mechanism
@ 2:55 - normal gears, but cut to engage on diagonals
@ 3:37 - SQUARE GEARS!
@ 3:41 - variable speed transfer
@ 3:46 - rotary to linear action with a 4 tooth cog

 

Several users have commented that these gears may be

on display at The Museum of Science and Industry in Chicago, IL.