Manufactured prior to 1939, these side delivery sickle mowers were extremely popular in their time. Originally horse drawn, this one has been modified to hitch to a tractor. Ground powered, in a heavy hay crop they required a fair amount of strength from the horses and were difficult to use when the ground was damp or wet, as the wheels were unable to gain traction.
This particular mower has markings unfamiliar to me, so I'm unable to state which model it is.
The open gears suggest that this is a fairly early model, probably pre 1920, as the hay crop tended to wrap around these gears on occasion (causing a lot of blue air in the vicinity of the mower while the unfortunate farmer unwrapped the hay from the gears), necessitating their being enclosed in later models.
Here's a
Farmall sales brochure, date unknown.