This constituted a simple series circuit with the battery current flowing through the wire, into the rail at the far end, and back through the rail to the battery.
(This; constituted; a simple series circuit with the battery current) (the battery current; flowing; through the wire; into the rail at the far end, and back through the rail to the battery)
This the battery current
constituted flowing
a simple series circuit with the battery current
through the wire into the rail at the far end, and back through the rail to the battery