Larry, A circle is used to irrigate an agricultural field. It has a pivot in the center and towers connected to it on wheels that have sprinklers. It revolves in a circle watering the ground. The end gun is a large sprinkler head on the end of the end tower ( to reach out as far as it can). Farm ground was typically (here) parceled out as quarter section pieces (square), so if you stick a circle in the middle of the square, you end up with four corners that are not irrigated by the circle. It is not uncommon to have fertilizer and or chemicals pumped in the system, down stream of the circle pump, to be ran through the circle (irrigation system). It is how most farm ground is irrigated here, in Eastern Washington, it didn't dawn on me, that may not be the case else were. Hope this helps.
Gale
