"Thanks guys. What's an AG unit?"
In ship's lingo the acronym "AG" stands for "Artificial Gravity". In TOS I heard at least twice a report, after the ship had been shaken and stirred, "AG Section, gravity is at 0.7" (unfortunately these reports are mixed into the center channel, so it's impossible to isolate these intercom reports
I had always thought these overhead beams to be such AG units, i.e. before ENTERPRISE's "In a Mirror, Darkly" double episode (where much of the action in part II takes place on the TOS USS Defiant -
since events occur in the mirror universe I had absolutely no problems with a previous Enterprise
) more or less canonically established the function.
A thing I found extremely interesting in that ENTERPRISE episode were the extra sets on the engineering deck levels (well, I think those were these enigmatic engineering deck levels) we never saw before:
Here we have a corridor I believe to run the warp drive plasma to the pylons (the plasma tubes are left and right behind the corridor walls): http://ent.trekcore.com/gallery/albu...arkly2_208.jpg
Then, there is this one I believe to occupy the aft of the two decks (or levels) below the engine room: http://ent.trekcore.com/gallery/albu...arkly2_308.jpg
At first I thought it looked too modern but there was a familiar feel to the angles of the walls. Compare to this screencap from "The Naked Time" and the energizers / reactors on the side: http://tos.trekcore.com/hd/albums/1x...timehd1022.jpg
I believe these ENT walls either to be energizers / reactors or protective walls for these (note that even the hatches on these walls correspond to what appear to be control elements on the TOS energizers
). Makes me wonder if these energizers we've seen standing in the engine room (at different spots in Season One) are supposed to be fixed to the floor or have merely been lifted up from one of the lower levels for maintenance...