A bull's-eye is a type of lamp or lantern that was commonly used in the 18th century. Fisherman often used bull's-eyes on their boats.
A bull's-eye was a metal lantern, usually made of tin, that was distinguished by its glass lens, which allowed light to be focused in a particular direction. This light could be covered or revealed by sliding a little panel open or closed. In other words, a bull's-eye was very much like an early 18th century flashlight. The earliest true flashlights used a similar glass lens, at the time called a "bull's-eye lens."