To determine how turtles respond to magnetic fields that exist in different parts of the ocean or to magnetic field elements (such as inclination and intensity) that they encounter while migrating, each hatchling was placed into a nylon-Lycra harness as shown below.

 

A monofilament line was connected to the harness and each turtle was tethered to an electronic tracking system in the center of a circular pool of water. Turtles could therefore swim in any direction while the tracking system monitored the direction toward which the turtle swam. This information was relayed to a computer in an adjacent room.

 The pool of water was surrounded by a large coil system (represented by the red box-like structure in the diagram below). The coil consisted of numerous strands of wire through which electrical current could be run. The coil was controlled by a computer and could produce Earth-strength magnetic fields with any inclination and intensity. It could also be used to produce magnetic fields that match those found at any location along the migratory route of the loggerheads.