What state mr.jones went to bed in

Mr. Jones went to bed drunk.

Mr. Jones, of the Manor Farm, had locked the hen-houses for the night, but was too drunk to remember to shut the popholes. With the ring of light from his lantern dancing from side to side, he lurched across the yard, kicked off his boots at the back door, drew himself a last glass of beer from the barrel in the scullery, and made his way up to bed, where Mrs. Jones was already snoring.

Why was the ring of lihy form Mr.Jones, so lantern dancing from side to side?