It appears that the left gear is the driving gear and the right is the driven. This means that the angular speed of the right gear is the ratio of the left radius to the right radius (speed_right = speed_left*radius_left/radius_right). Because the angular speed of the left gear is constant the only change to the angular speed of the right will come from the changing radius ratio of the two gears.
This behavior can be seen a bit more clearly with nautilus gears that have constantly changing radii.
This behavior can be seen a bit more clearly with nautilus gears that have constantly changing radii.