At the second, remote switch the two wires would come together to be a single supply wire again.
Finally this supply wire would be routed from the second switch to the light fixture, and then a single return wire would take the shortest path through the building back to the fusebox.
The knobs separated the wire from potentially combustible framework, facilitated changes in direction, and ensured that wires were not subject to excessive tension.
Because the wires were suspended in air, they could dissipate heat well.
The foregoing is an example of the so-called Carter system wire layout.
In the case of modern North American split-phase power, the supply wires from two opposite single-phase circuit breakers are used to supply 240 V AC for high power devices.
Ceramic tubes were inserted into holes bored in wall studs or floor joists, and the wires were directed through them.
This kept the wires from coming into contact with the wood framing members and from being compressed by the wood as the house settled.
Ceramic bushings protected each wire entering a metal device box, when such an enclosure was used.
From there, a supply wire carries power to the light, and a return wire goes back to location of the second switch, and then retraces the path back to the fusebox.
For older K&T installations, the supply and return wires were not necessarily installed as a pair, and did not necessarily have to be near each other at all.
When a generic power outlet was desired, the wiring could run directly into the junction box through a tube of protective loom and a ceramic bushing.
Wiring devices such as light switches, receptacle outlets, and lamp sockets were either surface-mounted, suspended, or flush-mounted within walls and ceilings.
Ceramic tubes were sometimes also used when wires crossed over each other, for protection in case the upper wire were to break and fall on the lower conductor.