Density of lines of the magnetodynamic field arising from two parallel currents is more in the regions out of the distance between the two wires and then the molecular magnetic dipoles of air are pulled toward these regions and create a bigger pressure there which causes the two wires to be pushed (or to be attracted) toward each other. A similar reasoning applied conversely to two antiparallel currents justifies their repulsion arising from the created air pressure difference. Thus, most probably, railgun will not work very well in the absence of the air.\\ PACS: 41.90.+e
(23) Role of air pressure in the force between currents (pdf)