Cumulative song toasting successive sizes of drinking vessels, and those who serve them: "The quart pot, pint pot, half-a-pint, gill pot, half-a-gill, quarter-gill, nipperkin, and the brown bowl/Here's good luck, good luck, good luck to the barley mow."
The brown bowl is to get sick into.
Sharp cites a reference noting that this was sung after a pre-Christian ritual called "crying the neck". -PJS
It was my understanding (don't know where I heard it) that the "Barley Mow" was a challenge -- if you fail to sing it through accurately and/or in one breath, you have to take another drink and, perhaps, buy a round for the house. Naturally, things tend to go downhill rapidly after the first error. - RBW