What is a "swingman", what was his job, and why did he ride the roof?

[Huron&VirginianRy]

On the photo of the day today there is a "note the swingman atop the fourth car", SF 2-10-2 climbing Cajon Pass photo.

What is a "swingman", what was his job, and why did he ride the roof?

Sorry to be so ignorant.......first time I have seen this

 

[rrboomer]

The "Swingman" was the third brakeman, usually required by various State full crew laws.  He would be in the middle in areas of reduced visibility (curves, cuts, weather, for examples) to pass signs between the head and rear end of trains.  He was also an extra set of eyes/ears for enroute train defect inspection.  Thru areas like Cajon he was in the middle in case handbrakes were called for or to set/release retainers.

If there was work enroute the swingman would go to the head end to assist the head brakeman. If the engineer and conductor were feuding (quite often) the swingman was the sounding board/messenger boy.

rrb